Search

Neural plasticity of the brain or its ability to reorganize following injury has likely coincided with the successful clinical correction of severe deformity by facial transplantation since 2005. In this study, we present the cortical reintegration outcomes following syngeneic hemifacial vascularized composite allograft (VCA) in a small animal model. Specifically, changes in the topographic organization and unit response properties of the rodent whisker-barrel somatosensory system were assessed following hemifacial VCA. Clear differences emerged in the barrel-cortex system when comparing naïve and hemiface transplanted animals. Neurons in the somatosensory cortex of transplanted rats had decreased sensitivity albeit increased directional sensitivity compared with naïve rats and evoked responses in transplanted animals were more temporally dispersed. In addition, receptive fields were often topographically mismatched with the indication that the mismatched topography reorganized within adjacent barrel (same row-arc bias following hemifacial transplant). These results suggest subcortical changes in the thalamus and/or brainstem play a role in hemifacial transplantation cortical plasticity and demonstrate the discrete and robust data that can be derived from this clinically relevant small animal VCA model for use in optimizing postsurgical outcomes. NEW & NOTEWORTHY Robust rodent hemifacial transplant model was used to record functional changes in somatosensory cortex after transplantation. Neurons in the somatosensory cortex of face transplant recipients had decreased sensitivity to stimulation of whiskers with increased directional sensitivity vs. naive rats. Transplant recipient cortical unit response was more dispersed in temporary vs. naive rats. Despite histological similarities to naive cortices, transplant recipient cortices had a mix of topographically appropriate and inappropriate whiskered at barrel cortex relationships.

Macphail's "null hypothesis," that there are no differences in intelligence, qualitative, or quantitative, between non-human vertebrates has been controversial. This controversy can be useful if it encourages interest in acquiring a detailed understanding of how non-human animals express flexible problem-solving capacity ("intelligence"), but limiting the discussion to vertebrates is too arbitrary. As an example, we focus here on Portia , a spider with an especially intricate predatory strategy and a preference for other spiders as prey. We review research on pre-planned detours, expectancy violation, and a capacity to solve confinement problems where, in each of these three contexts, there is experimental evidence of innate cognitive capacities and reliance on internal representation. These cognitive capacities are related to, but not identical to, intelligence. When discussing intelligence, as when discussing cognition, it is more useful to envisage a continuum instead of something that is simply present or not; in other words, a continuum pertaining to flexible problem-solving capacity for "intelligence" and a continuum pertaining to reliance on internal representation for "cognition." When envisaging a continuum pertaining to intelligence, Daniel Dennett's notion of four Creatures (Darwinian, Skinnerian, Popperian, and Gregorian) is of interest, with the distinction between Skinnerian and Popperian Creatures being especially relevant when considering Portia . When we consider these distinctions, a case can be made for Portia being a Popperian Creature. Like Skinnerian Creatures, Popperian Creatures express flexible problem solving capacity, but the manner in which this capacity is expressed by Popperian Creatures is more distinctively cognitive., (Copyright © 2020 Cross, Carvell, Jackson and Grace.)

There is considerable evidence for computationally complex behavior, that is, behavior that appears to require the equivalent of mathematical calculation by the organism. Spatial navigation by path integration is perhaps the best example. The most influential account of such behavior has been Gallistel's (1990) computational-representational theory, which assumes that organisms represent key environmental variables such as direction and distance traveled as real numbers stored in engrams and are able to perform arithmetic computations on those representations. But how are these computations accomplished? A novel perspective is gained from the historical development of algebra. We propose that computationally complex behavior suggests that the perceptual system represents an algebraic field, which is a mathematical concept that expresses the structure underlying arithmetic. Our field representation hypothesis predicts that the perceptual system computes 2 operations on represented magnitudes, not 1. We review recent research in which human observers were trained to estimate differences and ratios of stimulus pairs in a nonsymbolic task without explicit instruction (Grace, Morton, Ward, Wilson, & Kemp, 2018). Results show that the perceptual system automatically computes two operations when comparing stimulus magnitudes. A field representation offers a resolution to longstanding controversies in psychophysics about which of 2 algebraic operations is fundamental (e.g., the Fechner-Stevens debate), overlooking the possibility that both might be. In terms of neural processes that might support computationally complex behavior, our hypothesis suggests that we should look for evidence of 2 operations and for symmetries corresponding to the additive and multiplicative groups. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Rats and mice are able to perform a variety of subtle tactile discriminations with their mystacial vibrissae. Increasingly, the design and interpretation of neurophysiological and behavioral studies are inspired by and linked to a more precise understanding of the detailed physical properties of the whiskers and their associated hair follicles. Here we used a piezoelectric sensor (bimorph) to examine how contact forces are influenced by the geometry of individual whisker hairs. For a given point along a whisker, bimorph signals are linearly related to whisker movement velocity. The slope of this linear function, called velocity sensitivity (VS), diminishes nonlinearly as whisker diameter decreases. Whiskers differ in overall length, thickness, and proximal-distal taper. Thus VS varies along an individual whisker and among different whiskers on the mystacial pad. Thinner, shorter whiskers, such as those located rostrally in rats and those in mice, have lower overall VSs, rendering them potentially less effective for mediating discriminations that rely on subtle velocity cues. The nonlinear effect of diameter combined with the linear effect of arc length produces radial distance tuning curves wherein small differences in the proximal-distal location of impacts yields larger differences in signal magnitude. Such position-dependent cues could contribute to the localization of objects near the face. Proximal-to-distal changes in contact location during whisking sweeps could also provide signals that aid texture discrimination. NEW & NOTEWORTHY This study describes the geometry of facial whiskers distributed across the mystacial pad with emphasis on velocity encoding of object strikes. Findings indicate how the shapes, lengths, and thicknesses of individual hairs can contribute to sophisticated vibrissa-based tactile discrimination., (Copyright © 2017 the American Physiological Society.)

Evarcha culicivora, an East African salticid spider, is a mosquito specialist and it is also a plant specialist, with juveniles visiting plants primarily for acquiring nectar meals and adults visiting plants primarily as mating sites. The hypothesis we consider here is that there are ontogenetic shifts in cognition-related responses by E. culicivora to plant odour. Our experiments pertain to cross-modality priming effects in three specific contexts: executing behaviour that we call the 'visual inspection of plants' (Experiment 1), adopting selective visual attention to specific visual targets (Experiment 2) and becoming prepared to respond rapidly to specific visual targets (Experiment 3). Our findings appear not to be a consequence of salient odours in general elevating E. culicivora's motivation to respond to salient visual stimuli. Instead, effects were specific to particular odours paired with particular visual targets, with the salient volatile plant compounds being caryophyllene and humulene. We found evidence that prey odour primes juveniles and adults to respond to seeing specifically prey, mate odour primes adults to respond to seeing specifically mates and plant odour primes juveniles to respond to seeing specifically flowers. However, plant odour appears to prime adults to respond to seeing specifically a mate associated with a plant., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The rodent whisker/trigeminal system, characterized by high spatial and temporal resolution, provides an experimental model for developing new therapies for improving sensory functions of damaged peripheral nerves. Here, we use controlled whisker stimulation and single-unit recordings of trigeminal ganglion cells to examine in detail the nature and time course of functional recovery of mechanoreceptive afferents following nerve transection with microsurgical repair of the infraorbital nerve (ION) branch of the trigeminal nerve in adult rats. Response measures include rapid vs. slow adaptation, firing rate, interspike intervals, latency, and angular (directional) tuning. Whisker-evoked responses, readily observable by 3 wk post-transection, recover progressively for at least the next 5 wk. All cells in transected animals, as in control cases, responded to deflections of single whiskers only, but topography within the ganglion was clearly disrupted. The time course and extent of recovery of quantitative response measures were receptor dependent. Cells displaying slowly adapting (SA) properties recovered more quickly than rapidly adapting (RA) populations, and for some response measures-notably evoked firing rates-closely approached or attained control levels by 8 wk post-transection. Angular tuning of RA cells was slightly better than control units, whereas SA tuning did not differ from control values. Nerve conduction times and refractory periods, examined separately using electrical stimulation of the ION, were slower than normal in all transected animals and poorly reflected recovery of whisker-evoked response latencies and interspike intervals. Results underscore the need for multiple therapeutic strategies that target different aspects of functional restitution following peripheral nerve injury., (Copyright © 2016 the American Physiological Society.)

Neonatal whisker trimming followed by adult whisker regrowth leads to higher responsiveness and altered receptive field properties of cortical neurons in corresponding layer 4 barrels. Studies of functional thalamocortical (TC) connectivity in normally reared adult rats have provided insights into how experience-dependent TC synaptic plasticity could impact the establishment of feedforward excitatory and inhibitory receptive fields. The present study employed cross-correlation analyses to investigate lasting effects of neonatal whisker trimming on functional connections between simultaneously recorded thalamic neurons and regular-spike (RS), presumed excitatory, and fast-spike (FS), presumed inhibitory, barrel neurons. We find that, as reported previously, RS and FS cells in whisker-trimmed animals fire more during the earliest phase of their whisker-evoked responses, corresponding to the arrival of TC inputs, despite a lack of change or even a slight decrease in the firing of thalamic cells that contact them. Functional connections from thalamus to cortex are stronger. The probability of finding TC-RS connections was twofold greater in trimmed animals and similar to the frequency of TC-FS connections in control and trimmed animals, the latter being unaffected by whisker trimming. Unlike control cases, trimmed RS units are more likely to receive inputs from TC units (TCUs) and have mismatched angular tuning and even weakly responsive TCUs make strong functional connections on them. Results indicate that developmentally appropriate tactile experience early in life promotes the differential thalamic engagement of excitatory and inhibitory cortical neurons that underlies normal barrel function., (Copyright © 2015 the American Physiological Society.)

Using Evarcha culicivora, an East African jumping spider (Salticidae), we investigate how nectar meals function in concert with predation specifically at the juvenile stage between emerging from the egg sac and the first encounter with prey. Using plants and using artificial nectar consisting of sugar alone or sugar plus amino acids, we show that the plant species (Lantana camara, Ricinus communis, Parthenium hysterophorus), the particular sugars in the artificial nectar (sucrose, fructose, glucose, maltose), the concentration of sugar (20%, 5%, 1%) and the duration of pre-feeding fasts (3 days, 6 days) influence the spider's prey-capture proficiency on the next day after the nectar meal. However, there were no significant effects of amino acids. Our findings suggest that benefits from nectar feeding are derived primarily from access to particular sugars, with fructose and sucrose being the most beneficial, glucose being intermediate and maltose being no better than a water-only control.

Muscle-derived stem-cell (MDSC) transplantation presents a promising method for the treatment of muscle injuries. This study investigated the ability of exercise to enhance MDSC transplantation into the injured muscle. Mice were divided into four groups: contusion + phosphate-buffered saline (C + PBS; n = 14 muscles), C + MDSC transplantation (n = 12 muscles), C + PBS + treadmill running (C + PBS + TM; n = 17 muscles), and C + MDSC + TM (n = 13 muscles). One day after injury, the TM groups began running for 1 or 5 weeks. Two days after injury, muscles of C + MDSC and C + MDSC + TM groups were injected with MDSCs. One or 5 weeks later, the number and differentiation of transplanted MDSCs, myofiber regeneration, collagen I formation, and vascularity were assessed histologically. In vitro, MDSCs were subjected to mechanical stimulation, and growth kinetics were quantified. In vitro, mechanical stimulation decreased the MDSC population doubling time (18.6 +/- 1.6 h) and cell division time (10.9 +/- 0.7 h), compared with the controls (population doubling time: 23.0 +/- 3.4 h; cell division time: 13.3 +/- 1.1 h) (p = 0.01 and 0.03, respectively). In vivo, 5 weeks of TM increased the myogenic contribution of transplanted MDSCs, compared with the controls (p = 0.02). C + MDSC, C + PBS + TM, and C + MDSC + TM demonstrated decreased fibrosis at 5 weeks, compared with the C + PBS controls (p = 0.00, p = 0.03, and p = 0.02, respectively). Results suggest that the mechanical stimulation favors MDSC proliferation, both in vitro and in vivo, and that exercise enhances MDSC transplantation after injury.

Background and Purpose: Motor symptoms of Parkinson's disease (PD) are typically assessed using clinical scales such as the Unified Parkinson's Disease Rating Scale, but clinical scales are insensitive to subtle changes early in the disease process. The goal of this project was to use current sensing technology to develop a quantitative assessment tool to document fine motor deficits in PD based on the ability to control grip force output. The assessment was designed to challenge deficits commonly encountered as a result of PD, including dual-task performance of a motor task and a cognitive task simultaneously., Methods: Two force sensors were used to measure the isometric pinch grip force between the thumb and index finger in 30 individuals with PD and 30 control participants of similar age without disability. Participants performed a target force tracking task with each of two different target waveforms (sinusoidal or pseudorandom) under each of three different cognitive load conditions (none, subtract 1, and subtract 3). Dependent variables calculated from the force sensor data included root mean square error, tremor integral, and lag., Results: In general, individuals with PD showed significantly less accuracy in generating the target forces as shown by larger root mean square error compared with controls (P < 0.001). They also showed greater amounts of tremor and lag compared with controls (P = 0.001 and <0.001, respectively). Deficits were more pronounced during the cognitive multitasking component of the test., Discussion and Conclusions: These results will serve as a preliminary work for the development of a clinical biomarker for PD that may help to identify subtle deficits in fine motor control early in the disease process and facilitate tracking of disease progression with time.

Background: The ability to achieve optimal functional recovery is important in both face and hand transplantation. The purpose of this study was to develop a functional rat hemifacial transplant model optimal for studying both functional outcome and cortical reintegration in composite tissue allotransplantation., Methods: Five syngeneic transplants with motor and sensory nerve appositions (group 1) and five syngeneic transplants without nerve appositions (group 2) were performed. Five allogeneic transplants were performed with motor and sensory nerve appositions (group 3). Lewis (RT1) rats were used for syngeneic transplants and Brown-Norway (RT1) donors and Lewis (RT1) recipients were used for allogeneic transplants. Allografts received cyclosporine A monotherapy. Functional recovery was assessed by recordings of nerve conduction velocity and cortical neural activity evoked by facial nerve and sensory (tactile) stimuli, respectively., Results: All animals in groups 1 and 3 showed evidence of motor function return on nerve conduction testing, whereas animals in group 2, which did not have nerve appositions, did not show electrical activity on electromyographic analysis (p < 0.001). All animals in groups 1 and 3 showed evidence of reafferentation on recording from the somatosensory cortex after whisker stimulation. Animals in group 2 did not show a cortical response on stimulation of the whiskers (p < 0.001)., Conclusion: The authors have established a hemiface transplant model in the rat that has several modalities for the comprehensive study of motor and sensory recovery and cortical reintegration after composite tissue allotransplantation.

A prominent feature of thalamocortical circuitry in sensory systems is the extensive and highly organized feedback projection from the cortex to the thalamic neurons that provide stimulus-specific input to the cortex. In lightly sedated rats, we found that focal enhancement of motor cortex activity facilitated sensory-evoked responses of topographically aligned neurons in primary somatosensory cortex, including antidromically identified corticothalamic cells; similar effects were observed in ventral posterior medial thalamus (VPm). In behaving rats, thalamic responses were normally smaller during whisking but larger when signal transmission in brainstem trigeminal nuclei was bypassed or altered. During voluntary movement, sensory activity may be globally suppressed in the brainstem, whereas signaling by cortically facilitated VPm neurons is simultaneously enhanced relative to other VPm neurons receiving no such facilitation.

Studies of the rodent whisker system indicate that somatosensory cortical circuitry operates at a millisecond timescale to transform sensory afferent signals from the thalamus. We measured axon conduction times and whisker-evoked responses of 48 thalamocortical (TC) neurons in the rat whisker-to-barrel pathway. Conduction times were derived from spike-triggered averages of local field potentials evoked in layer 4 cortical whisker-related barrels by the spontaneous firing of individual topographically aligned neurons in the ventral posterior medial thalamus. Conduction times varied fourfold, from 0.31 to 1.34 ms, and faster conducting TC neurons responded earlier and more robustly to controlled whisker deflections. Early arrival of highly responsive TC inputs, thought to contact inhibitory barrel neurons preferentially, could prime the cortical network, rendering it more selective for later-arriving signals.

We have developed a semi-automated technique for acquiring neurophysiological data during whisker-based tactile discriminative behavior. Water-deprived, blindfolded rats are tethered by means of a harness vest that permits them to contact a rough (250 micrometer grooves) or smooth discriminandum with only their vibrissae. Discriminanda are mounted on a motor-driven carousel, and the rat indicates its choice (rough, smooth) by licking either a right or left water port located near the carousel. A narrow light beam detects general proximity of the animal's nose to the discriminandum, although actual whisker contact is monitored by a SuperVHS camera and measured offline using field-by-field videographic analysis. Rats can be trained within 3-6 weeks at which time they perform 100-150 trials/day at a level of 80% correct. Unit recording from the somatosensory cortex reveals that neurons increase their firing upon whisker contact of a discriminandum and that firing remains elevated during several hundred milliseconds of ongoing contact, even with the smooth surface. Nevertheless, despite the animal's ability to distinguish the rough and smooth surfaces, overall neuronal firing rates were indistinguishable for the two surfaces. In some cases, temporal firing patterns differed, although not in a consistent way across recording sites.

Background and Purpose: People with peripheral vestibular pathology demonstrate motor impairments when responding and adapting to postural platform perturbations and during performance of sit-to-stand and locomotor tasks. This study investigated the influence of unilateral peripheral vestibular hypofunction on voluntary arm movement., Subjects and Methods: Subjects without known neurological impairments and subjects with vestibular impairments performed 3 voluntary arm movements: an overhead reach to a target, a sideward reach to a target, and a forward flexion movement through 90 degrees. Subjects performed these tasks under precued and choice reaction time conditions. During all tasks, body segment motion was measured. Head velocity measurements were calculated for the side task only., Results: Subjects with vestibular loss restricted upper body segment motion within the frontal and transverse planes for the 90-degree and overhead tasks. Average angular head velocity was lower for the group with vestibular hypofunction. Task uncertainty (the introduction of a choice reaction time paradigm) differentially influenced the groups regarding head velocity at target acquisition., Discussion and Conclusion: Individuals with vestibular loss altered their performance of voluntary arm movements. Such alterations may have served to minimize the functional consequences of gaze instability.

Physiological studies of the rodent somatosensory cortex have consistently described considerable heterogeneity in receptive field properties of neurons outside of layer IV, particularly those in layers V and VI. One such approach for distinguishing among different local circuits in these layers may be to identify the projection target of neurons whose axon collaterals contribute to the local network. In vivo, this can be accomplished using antidromic stimulation methods. Using this approach, the axonal conduction properties of cortical efferent neurons are described. Four projection sites were activated using electrical stimulation: (1) vibrissal motor cortex, (2) ventrobasal thalamus (VB), (3) posteromedial thalamic nucleus (POm), and (4) cerebral peduncle. Extracellular recordings were obtained from a total of 169 units in 21 animals. Results demonstrate a close correspondence between the laminar location of the antidromically identified neurons and their anatomically known layer of origin. Axonal properties were most distinct for corticofugal axons projecting through the crus cerebri. Corticothalamic axons projecting to either VB or POm were more similar to each other in terms of laminar location and conduction properties, but could be distinguished using focal electrical stimulation. It is concluded that, once stimulation parameters are adjusted for the small volume of the rat brain, the use of antidromic techniques may be an effective strategy to differentiate among projection neurons comprising different local circuits in supra- and infragranular circuits.

This study used extracellular unit recordings in behaving animals to evaluate thalamocortical response transformations in the rat whisker-barrel system. Based on previous acute studies using controlled whisker stimulation, we hypothesized that in a cortical barrel adjacent (non-principal) whiskers exert a net inhibitory effect. In contrast, in thalamic barreloid neurons, the effects of neighboring whiskers should be net facilitatory. We evaluated these hypotheses by recording unit activity at 21 sites in 17 animals trained to explore a wire mesh screen with their whiskers. In the middle of the recording session, selected vibrissae were clipped close to the skin surface. The absence of whiskers surrounding the principal whisker was associated with a mean 20% increase in cortical activity and, conversely, a 37% decrease in the thalamic activity. Removal of the principal whisker resulted in a 50% decrease in cortical unit firing. Findings are consistent with the idea that, in the behaving animal, each barrel uses multi-whisker thalamic inputs and local inhibitory circuitry to sharpen the receptive field properties of its constituent neurons. Cortical disinhibition as a consequence of selective whisker removal is likely to be an important factor underlying altered receptive field properties in sensory-deprived animals.

This study compared voluntary movement strategies of patients with unilateral peripheral vestibular hypofunction with those of age-matched healthy control subjects. All subjects performed three voluntary movement tasks with their dominant upper extremity: a forward flexion arm movement through 90 degrees, a reach to an overhead target, and a reach to a side target. Subjects performed the movement tasks sitting and standing (Body Position), and under precued and choice reaction time (RT) conditions (Task Certainty). Measures of motor planning and movement execution included RT and movement time (MT), respectively. Statistical analysis included separate Group x Task Certainty x Body Position ANOVA calculations for each task. Across tasks, results suggested no between group differences for RT. A Task Certainty main effect for the side and overhead tasks indicated that the choice RT situation resulted in longer RTs as compared to the precued RT condition. Movement time differed between the two groups. Across all three voluntary movement tasks, vestibular impaired subjects moved more slowly than control subjects. Providing vestibular subjects with a precue did not bring MT performance to the level of controls. Body position influenced MT for the side task only. Across both groups of subjects, MT for the side task was longer when performed in the standing position. The results of this study suggest that individuals with unilateral peripheral vestibular hypofunction initiate voluntary movement responses with similar timing as control subjects, but require more time to complete the movement. Vestibular rehabilitation should include goal-directed movement and should address issues of movement speed.

Extracellular unit recordings were made at various depths within SmI barrel cortex of immobilized, sedated rats, in the presence and absence of titrated amounts of the GABA(A) receptor antagonist bicuculline methiodide (BMI). Principal and adjacent whiskers were moved singly, or in paired combination in a condition-test paradigm, to assess excitatory and inhibitory receptive field (RF) characteristics. Neurons were classified as regular- or fast-spike units, and divided into three laminar groups: supragranular, granular (barrel), and infragranular. BMI increased response magnitude and duration, but did not affect response latencies. The excitatory RFs of barrel units, which are the most tightly focused on the principal whisker, were the most greatly defocused by BMI; infragranular units were least affected. All three layers had approximately equal amounts of adjacent whisker-evoked, surround inhibition, but BMI counteracted this inhibition substantially in barrel units and less so in infragranular units. The effects of BMI were most consistent in the barrel; more heterogeneity was found in the non-granular layers. These lamina-dependent effects of BMI are consistent with the idea that between-whisker inhibition is generated mostly within individual layer IV barrels as a result of the rapid engagement of strong, local inhibitory circuitry, and is subsequently embedded in layer IV's output to non-layer IV neurons. The latter's surround inhibition is thus relatively resistant to antagonism by locally applied BMI. The greater heterogeneity of non-granular units in terms of RF properties and the effects of BMI is consistent with other findings demonstrating that neighboring neurons in these layers may participate in different local circuits.

Extracellular single-unit recordings were made in somatosensory cortical barrels of fentanyl-sedated rats. Whiskers were deflected singly or in paired combinations. Iontophoretically-applied (-)-baclofen disproportionately reduced weak responses, and phaclofen disproportionately increased them, resulting in more tightly focused or more broadly focused receptive fields, respectively. Both drugs had only minor effects on surround inhibition. In light of previous findings, we conclude that GABAA and GABAB mechanisms both act to enhance spatial contrast, but that the former plays a much greater role in enhancing temporal resolution.

1. Carbon fiber multibarrel glass microelectrodes were used to record extracellular single-unit activity during microiontophoretic application of gamma-aminobutyric acid (GABA) or bicuculline methiodide (BMI) onto layer IV barrel neurons in the somatosensory cortex of fentanyl-sedated rats. Excitatory and inhibitory aspects of the neurons' receptive fields were quantified with the use of controlled whisker stimuli. The principally activating whisker and one of its immediately adjacent neighbors were deflected alone or in paired combinations involving a condition-test paradigm. 2. Units were distinguished electrophysiologically on the basis of the time course of their action potential waveforms. Data were obtained from 26 regular-spike units (RSUs; presumed spiny stellate cells) and 7 fast-spike units (FSUs; presumed GABAergic neurons). An average of 15.0 nA of GABA produced a one-third to one-half reduction in RSU responses evoked by the maximally effective stimulus. An average of 8.7 nA of BMI was needed to counteract this reduction. This amount of BMI, in the absence of exogenous GABA, was found to increase average RSU and FSU responses by 98 and 53%, respectively, relative to predrug levels. 3. For RSUs, the BMI-induced twofold increase in responses evoked by moving the principal whisker at the neuron's best deflection angle was accompanied by an almost threefold increase in responses evoked by similarly moving an adjacent whisker. Disproportionately large percentage increases were also seen for responses to nonpreferred directions of principal and adjacent whisker movement. BMI thus effectively increased receptive field size and decreased angular tuning. Similarly, responses to stimulus offsets, which are normally smaller than ON responses, were increased proportionally more. 4. Predrug responses of FSUs were more vigorous than those of RSUs. However, FSUs showed a similar inverse relationship between percentage increase with BMI and initial response magnitude, although the proportional increases were less pronounced. 5. GABA, like BMI, had the greatest proportional effects on those responses that were initially smallest. It produced results opposite those of BMI, effectively decreasing receptive field size and sharpening angular tuning. 6. A previously described computational model of a barrel was tested for its ability to reproduce quantitatively the effects of BMI and GABA. The application of BMI was simulated by decreasing the strength of the inhibitory inputs onto the particular cell under study in the model network. GABA microiontophoresis was simulated by adding a constant hyperpolarizing voltage. The model RSUs and FSUs displayed proportional changes in response magnitude that were quantitatively similar to those of their biological counterparts. 7. Surround inhibition was greatly attenuated by BMI application, both for the real and simulated barrel neurons. Disinhibition was less pronounced for the former, perhaps because, unlike the simulated neurons, they also possess GABAB receptors, which are unaffected by BMI. 8. We conclude that the inhibitory receptive field properties of barrel neurons can be explained by intrabarrel inhibition and that the expansion of receptive field size and loss of angular tuning with BMI is due to an enhanced effectiveness of convergent, multi-whisker thalamocortical input. Examination of the model neurons' behavior suggests that the altered activity in response to GABA or BMI application, respectively, can be explained by the nonlinear effects of shifting somal membrane potential away from or toward the neuron's firing threshold.

Rats actively sweep their whiskers back and forth to locate and palpate objects within their immediate environment. Microstimulation studies in anesthetized rats have demonstrated the presence of a large vibrissal motor representation in agranular cortex. However, the manner in which motor cortex neurons contribute to whisking behavior in the awake animal is unknown. This study represents an initial investigation of the relationship between the activity of task-related neurons in vibrissal motor cortex and the electromyographic (EMG) activity of the deep vibrissal pad muscles in the awake, freely whisking rat. Each animal was gently held in an experimenter's hands while the animal whisked the air. A spring-loaded, metal microelectrode mounted in a removable, miniature microdrive provided stabile recordings of motor cortex unit activity. Fine-wire electrodes implanted in the mystacial pad simultaneously recorded facial muscle activity. Results showed that the discharge of task-related neurons was correlated with changing levels of muscle output. Unit discharge was related in a tonic or phasic-tonic fashion to EMG activity. No units were found to discharge rhythmically in a 1:1 fashion with the periodicity of the whisking pattern. These findings support a role for vibrissal motor cortex in the initiation and modulation of the overall level of mystacial pad muscular output, but not in the generation of bursts of EMG activity responsible for individual whisking sweeps.

Rats explore objects by rhythmically whisking them with their mystacial vibrissae. On two types of tactile discrimination tasks, macrogeometric and microgeometric, better performers palpated the discrimnanda for longer periods of time and used movement patterns that appeared to optimize whisking frequency bandwidth and the extent to which the vibrissae would be bent by object contact. On a task involving finely textured surfaces, good and poor performers differed in the temporal components of their whisking patterns, whereas the spatial domain was more important for animals palpating surfaces with widely separated features. These findings are consistent with increasing neurophysiological evidence that the central representation of the tactile periphery, in rodents and other mammals, is both integrative and dynamic.

1. Previous studies have demonstrated marked differences in the relative sizes of ON and OFF responses of neurons in the whisker/barrel system. In particular, OFF responses are unexpectedly large in thalamic neurons. Extracellular unit recordings were used to examine whether varying the time between stimulus onset and offset differently affects OFF responses of neurons in the trigeminal ganglion, ventrobasal thalamus, and somatosensory cortical layer IV. Controlled whisker stimuli were used to deflect individual vibrissal hairs in different directions. We hypothesized that, in part because of the gradual waning of central inhibition evoked by stimulus onset, OFF responses of thalamic and cortical neurons but not trigeminal ganglion cells would increase in size with longer duration stimuli, with relative changes being greatest in the cortex. 2. OFF response magnitudes for thalamic and cortical neuronal populations increased as the stimulus duration was increased from 200 to 1,400 ms. Increases were greater at nonoptimal deflection angles. Similarly, individual cells having smaller OFF responses for the short-duration stimulus tended to display proportionately greater increases when the stimulus was lengthened. OFF responses of trigeminal ganglion cells were largely unaffected by stimulus duration. 3. Barrel neurons were subclassified as regular-spike units (RSUs) or fast-spike units (FSUs) on the basis of the time course of their action potentials. ON and OFF responses were smaller in the former and, when the stimulus was lengthened, percentage increases in their OFF responses were greater than those in FSUs. Results illustrate nonlinear transformations of the thalamic input signal by RSUs, which are presumed to be excitatory barrel neurons, and extend previous findings of response similarities between thalamocortical units (TCUs) and FSUs, the latter of which are thought to be inhibitory. 4. The time course of OFF response suppression in cortical neurons suggests that stimulus onset evokes central inhibition having two components, a potent one lasting several tens of milliseconds and a weaker one lasting many hundreds of milliseconds. Background activity levels in cortex and thalamus were diminished for > or = 1,800 ms after whisker movement. 5. For TCUs, 200-ms stimuli were less likely than 1,400-ms stimuli to elicit an OFF response, but when responses occurred they consisted of a greater number of spikes timed closer together. By contrast, the 200-ms stimulus OFF responses of the RSUs and FSUs displayed longer interspike intervals than did their 1400-ms responses, with no change in the number of spikes per response.(ABSTRACT TRUNCATED AT 400 WORDS)

A "barrel" is an interconnected network of layer IV neurons that is an important component of a functional cortical column in the whisker area of the rodent primary somatosensory cortex. The present study was undertaken in order to resolve apparently conflicting findings from single-unit studies of barrel neurons conducted in rats maintained under different anesthetic conditions. Multiunit responses to controlled deflections of mystacial vibrissae were recorded from the whisker/barrel cortex of awake, undrugged rats, and responses at the same recording site were reexamined after the animal was anesthetized with urethane. In contrast to the awake condition, stimulus-evoked responses under urethane were characterized by a large late component. Such effects were more pronounced for deflections of noncolumnar or "adjacent" whiskers than for the columnar whisker. Latencies to peak responses were virtually identical for the columnar whisker in awake and urethane states (11.9 vs 11.8 ms) but were considerably longer for adjacent whisker deflections in urethane-anesthetized animals (15.5 vs 29.0 ms). The magnitudes of adjacent whisker responses, relative to the response evoked by the columnar whisker, varied with the laminar location of the recording site in awake but not in urethane-anesthetized animals; in awake rats, receptive fields were clearly smallest in the layer IV barrels. Results in the awake condition confirm those of previous studies conducted in unanesthetized or lightly sedated animals, and data obtained with urethane are comparable to others' results in urethane-anesthetized rats. The former have important implications for how barrel cortex processes information in behaving animals.

Neurophysiological and 2-deoxyglucose (2DG) studies of the rodent whisker barrel cortex have demonstrated asymmetries in its functional organization. To examine the possibility that the activity gradients observed in metabolic studies can be attributed to subtle rostral-caudal and dorsal-ventral asymmetries in electrophysiologically measured surround or cross-whisker inhibition, we compared 2DG results with predictions generated from quantitative single-cell receptive field data. Despite differences in the two experimental approaches, there is remarkable agreement between the findings. (1) The distribution of 2DG activity declines across the barrel cortex of the behaving animal from anteromedial barrels to posterolateral barrels, and is qualitatively and quantitatively similar to the values predicted from neurophysiology. (2) The strength of surround inhibition in barrel neurons predicts the twofold increase in activation of the C3 barrel following acute clipping of adjacent whiskers. And (3) within a cortical column, the decrease in metabolic activity associated with adjacent whisker stimulation is greatest in layer IV and least in the infragranular layers; this corresponds to the laminar distribution of inhibitory interactions observed electrophysiologically.

Cinematographic measurements of whisker movements generated by behaving rats were compared with electromyographic (EMG) activity recorded simultaneously from mystacial pad musculature. Muscle activity consisted of repetitive bursts, each of which initiated a "whisking" cycle consisting of a protraction followed by a retraction. Protraction amplitude and velocity were directly proportional to the amount of EMG activity during forward whisker movement. Overtime, the intensity of muscle discharge determined the set point about which the vibrissae moved; higher levels of muscle activity resulted in a greater degree of overall whisker protraction. These findings are consistent with the known anatomy of the facial musculature and underscore the importance of whisker protraction in the acquisition of tactile information by the vibrissae.

The response properties of 123 trigeminal ganglion neurons were studied, using controlled whisker deflections in different directions. When the distal end of the whisker was initially displaced 5.7 degrees (1 mm) from its neutral position, 81% of the cells responded with statistically more spikes/stimulus to movements in one to three of eight cardinal (45 degrees increment) directions than to the others. The more directionally selective the cell, the more vigorous was its response. On the basis of statistical criteria, 75% of the cells were classified as slowly adapting, 25% as rapidly adapting. A number of quantitative analyses indicated that slowly adapting units respond more selectively than rapidly adapting cells to the direction of whisker movement. Differences in directional sensitivities of rapidly and slowly adapting cells appear to parallel differences between their putative mechanoreceptive endings and the relationships between those endings and the vibrissa follicle's structure. Comparisons between the response properties of peripheral and central neurons in the vibrissa-lemniscal system indicate that the afferent neural signal is progressively and substantially transformed by mechanisms that function to integrate information from different peripheral receptors and from different, individual vibrissae.

Axonal tracing techniques were used to examine the distribution of corticothalamic projection neurons in relation to the organization of the thalamocortical recipient zones in the whisker representation of the rat first somatic sensory cortex. Following injection of horseradish peroxidase into the physiologically defined vibrissa area in the ventrobasal complex of the thalamus, labeling in the cortex had a columnar appearance. Dense patches of anterograde labeling were located within the centers of the layer IV barrels and extended superficially through lamina III; the septa between barrels contained considerably less reaction product. Retrogradely labeled neurons were observed in lower layer V and layer VI where they were concentrated preferentially deep to the barrel centers. Regions deep to the septa displayed less overall labeling and a lower relative number of thalamic projecting neurons. Zones having the larger numbers of retrogradely labeled cells also contained terminallike labeling of either corticothalamic or thalamocortical origin. Following an injection that included the posterior group medial to the ventrobasal complex, anterograde labeling in layer IV was located largely in the septa. In conjunction with previous findings concerning the origin and termination of other projection systems in the barrel cortex, these results suggest that a vibrissal column contains a central core zone intimately linked with the ventrobasal thalamus that is bounded by narrower regions of more diverse inputs and outputs that form an interface between adjacent cortical columns.

The somatotopic organization of the parietal cortex of barbiturate-anesthetized, adult mice was studied using tungsten microelectrodes. A complete representation of the contralateral face and body occupying approximately 4.0-4.5 mm2 was found immediately posterior and lateral to the representation of the face in the first somatosensory area (SI). Within this second somatosensory area (SII), the following findings were made: A relatively large region is devoted to representations of the paws and face, especially the sinus hairs associated with the anterior upper lip and mystacial vibrissae. Receptive fields on these body regions are among the smallest found in SII, though larger than corresponding receptive fields in SI. In particular, vibrissae receptive fields always include at least several adjacent whiskers, and paw receptive fields always include at least two adjacent digits. In regions representing proximal body parts, receptive fields are considerably larger, may include both contralateral and ipsilateral limb or trunk surfaces, and sometimes include the entire body and face. Responses to both somatosensory and auditory stimulation were consistently found in the body (i.e., trunk and limb) representation, but rarely found in the face region. The face is represented most anteriorly, and the hindlimb and tail most posteriorly. Forepaw and hindpaw digits and anterior aspects of the face (e.g., perioral sinus hairs and the incisors) are represented laterally, while the back, caudal head, and mystacial vibrissae are represented medially. Within SII, therefore, a "musculus" can be viewed as having an upright body orientation with the face area bordering the face representation within SI. By comparison with SI, SII is characterized by a less pronounced layer IV, which is of irregular thickness and packing density, and by less uniformity in the layering of pyramidal cells in lamina V. In addition, SII is generally thicker from pia to white matter than SI. These results are in general accord with earlier findings from evoked potential studies in mice, but are at variance with recent reports in mice and rats that the mystacial vibrissae have only a minimal, or no, representation within SII. Indeed, the present findings suggest that the representation of the whiskers in SII may have a specialized function paralleling that in SI.

Thalamic and corticocortical connections of the second somatic sensory area (SII) in the mouse cerebral cortex were investigated by means of the retrograde transport of horseradish peroxidase. Focal injections of the enzyme were made in physiologically determined locations within the parietal cortex. Results show that SII receives substantial inputs from topographically appropriate regions within the ipsilateral ventrobasal nucleus and from the ipsilateral posterior group. The limb representation, which was previously found to be responsive to auditory stimulation, received inputs also from the medial division of the medial geniculate body. The SII face representation, which is largely unresponsive to auditory stimuli, received little or no input from the medial geniculate body. SII injections yielded retrograde labeling in the topographically appropriate region in the first somatic sensory area (SI), and SI injections retrogradely labeled cells in SII in a pattern consistent with previous electrophysiological maps. Homotypical regions within SI and SII therefore appear to be reciprocally interconnected. SII also receives inputs from the ipsilateral motor cortex and from contralateral SI and SII. Finally, injections into the SI paw but not face regions yielded retrograde labeling in the thalamic ventrolateral nucleus. Thus, the distal limb representations in SI and SII each receive inputs from a third major relay nucleus (i.e., medial geniculate to SII, ventrolateral nucleus to SI) whereas the face representations do not. These results indicate a close functional interrelationship between homotypical areas in SI and SII, though the two areas differ in several important respects. It is proposed that SII in mice may complement the function of SI by helping to define the overall sensory context in which detailed tactile discriminations are made.

Intracellular recordings from rat somatic sensory vibrissa/barrel cortex demonstrate that whisker displacements evoke short latency excitatory postsynaptic potentials followed by longer lasting inhibitory potentials. The time course and whisker-related spatial distribution of the potentials represent synaptic correlates of the integration of whisker inputs observed in extracellular studies.

1. Extracellular single-unit recordings and controlled whisker stimuli were used to compare response properties between cells in the "barreloids" of the thalamic ventrobasal complex and those in the cytochrome oxidase-rich centers of the "barrels" in the first somatic sensory cortex. Individual vibrissae were deflected alone or in paired combination involving the neuron's maximally excitatory whisker and an adjacent one in the same or neighboring whisker rows. Quantitative data were derived from 135 thalamocortical unit's (TCUs), 242 "regular-spike" barrel units (RSUs), and 16 "fast-spike" barrel units (FSUs) recorded in 26 normal adult rats. 2. Compared with TCUs, RSUs displayed lower rates of spontaneous activity and responded less vigorously to whisker stimuli. Proportionally, more than twice as many TCUs as RSUs responded in slowly adapting fashion to at least one angular direction of whisker displacement. Discharges of slowly adapting TCUs were approximately 3.5 times greater than those of slowly adapting RSUs. 3. Proportionally, about twice as many TCUs than RSUs responded selectively to whisker movements in different angular directions. 4. Cells in the thalamus responded more vigorously to a larger number of whiskers than RSUs in the cortex. Depending on the stimulus conditions, two to three times more TCUs than RSUs were excited by two or more whiskers. 5. Following displacement of an adjacent whisker, unit discharges to subsequent deflections of the maximally excitatory whisker were reduced in a time-dependent fashion. The time course of response suppression was similar in TCUs and RSUs, but inhibitory interactions between adjacent whiskers were observed much less often in the thalamus. A cyclic pattern of stimulus-evoked excitation/inhibition characterizes responses in the cortical barrels but is considerably less pronounced in the thalamic barreloids. 6. The presence and/or degree of response suppression depended on which adjacent whisker was stimulated and on the angular direction of that whisker's movement. For individual TCUs, some adjacent whiskers evoked inhibition, others did not. The vast majority of RSUs displayed response suppression to all adjacent whiskers. Unlike receptive fields of TCUs, those of RSUs have small--i.e., single-whisker--excitatory centers with potent and symmetrical inhibitory surrounds. 7. Fast-spike units in the barrels displayed the greatest spontaneous and stimulus-evoked activities and were the least selective for whisker movements at different angular directions. FSUs had the largest excitatory receptive fields; 100% responded to two or more vibrissae.(ABSTRACT TRUNCATED AT 400 WORDS)