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Arborization of single corticocortical (CC) axons projecting from the parietal cortex to the motor cortex (Mx) was analysed using an intraaxonal staining technique in the cat. Stem axons arising from cell bodies in area 5 ramified repeatedly into numerous terminal branches in the Mx, forming 2-6 patches (0.2-0.8 mm in diameter) separated by a terminal-free gap. Axon terminals were distributed mainly in layers II and III and sparsely in layers V, VI and I. This feature is quite similar to that of thalamocortical axons and other corticocortical fibres. Thus the patchy organization may be a basic input structure for afferents of the Mx and play a role in generation of adequate motor output patterns in the Mx.

Morphology of single axons of tectospinal (TS) neurons was investigated by intraaxonal injection of horseradish peroxidase (HRP) at the upper cervical spinal cord of the cat. TS axons were electrophysiologically identified by their direct responses to stimulation of the contralateral superior colliculus (SC). None of these axons responded to thoracic stimulation at Th2. Three-dimensional reconstructions of the axonal trajectories were made from 20 well-stained TS axons at C1-C3. Cell bodies of these axons were located in the intermediate or deep layers of the caudal two-thirds of the SC. Usually, TS axons had multiple axon collaterals, and up to seven collaterals were given off per stem axon [2.7 ± 1.6 (mean ± S.D.); n = 20]. Collaterals had simple structures and ramified a few times mainly in the transverse plane. The number of terminals for each collateral was small. These collaterals terminated in the lateral parts of laminae V–IX, mainly in laminae VI, VII, and VIII. There were usually gaps free from terminal arborizations between adjacent collaterals, because the rostrocaudal spread of each collateral (mean = 700 μm) was narrower than the intercollateral interval (mean = 2,500 μm). Seven of the 19 TS axons had terminals in the lateral parts of laminae V–VIII, with little projection to lamina IX, and the other 12 axons had terminals in lamina IX besides the projection to the lateral parts of laminae V–VIII. Axon terminals in lamina IX did not appear to make contacts with the somata or proximal dendrites of retrogradely labeled motoneurons, but contacts were found with the somata of counterstained interneurons in the lateral parts of laminae V–VIII. Three spinal interneurons (two in lamina VIII and one in lamina V at C1) that received monosynaptic excitation from the SC were stained, and their axonal trajectories were reconstructed. They had multiple axon collaterals at C1-C2 and mainly projected to laminae VIII and IX, with smaller projections to lamina VII. Many axon terminals of the interneurons were found in multiple neck motor nuclei, where some of them made contacts with retrogradely labeled motoneurons. The present finding provides evidence that the direct TS projection to the spinal cord may influence activities of multiple neck muscles, mainly via spinal interneurons, and may play an important role in control of head movement in parallel with the tectoreticulospinal system. © 1996 Wiley-Liss, Inc.

1. In the parietal cortex (Px, areas 5 and 7), the organization and characteristics of cerebellar and cerebral inputs and their effects on efferent neurons were investigated with the use of intracellular and extracellular recording techniques in the anesthetized cat. 2. Evoked field potential analysis revealed that two regions of the Px, the caudal bank of the ansate sulcus (Ans. S.) and the crown of the suprasylvian gyrus (Ssyl. G.), received converging input from the dentate and the interpositus nucleus. The cerebellar input to the caudal bank of the Ans. S. was relayed via the ventrolateral region of the ventroanterior-ventrolateral (VA-VL) complex of the thalamus, whereas the cerebellar input to the crown of the Ssyl. G. was relayed via the dorsomedial region of the VA-VL complex. 3. A total of 176 neurons was recorded intracellularly in the Px to examine inputs from the cerebellum. Of these, 72 neurons were corticocortical neurons projecting to the motor cortex (Mx), and 48 were corticofugal neurons to the pontine nucleus (PN). Intracellular staining with horseradish peroxidase revealed that the former corticocortical neurons were layer III pyramidal neurons and the latter corticofugal neurons were layer V pyramidal neurons. 4. Stimulation of the brachium conjunctivum (BC) produced di- or polysynaptic excitatory postsynaptic potentials (EPSPs) in corticocortical neurons projecting to the Mx and corticofugal neurons to the pontine nucleus in the Px. The characteristics of BC-evoked EPSPs were different between the bank of the Ans. S. and the crown of the Ssyl. G. In the bank of the Ans. S., the slope of the rising phase of the BC-evoked EPSPs was steeper, and their minimum latency was shorter by 0.8 ms than those in the crown of the Ssyl. G. These differences may reflect differences in the terminal distribution and conduction velocity of the thalamocortical fibers relaying cerebellar input to these two parietal areas. 5. Stimulation of the Mx produced mono- or disynaptic EPSPs in both corticocortical neurons projecting to the Mx and corticofugal neurons projecting to the pontine nucleus in the Px. For each neuron, effective sites for inducing EPSPs were distributed very widely and sometimes covered both areas 4 and 6. Extensive corticocortical projection from the Mx to the Px was confirmed by injection of an anterograde tracer into the Mx. 6. These data indicate that neurons in the Px receive inputs from both the cerebellum and the Mx and send outputs to the Mx and the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)

We propose a new method to provide a functional interpretation of motor commands (i.e., muscle activities) and their relationship to movement kinematics. We evaluated our method by analyzing the motor commands of normal controls and patients with cerebellar disorders for visually guided tracking movement of the wrist joint. Six control subjects and six patients with cerebellar disorders participated in this study. We asked the subjects to perform visually guided smooth tracking movement of the wrist joint with a manipulandum, and recorded the movements of the wrist joint and activities of the four wrist prime movers with surface electrodes. We found a symmetric relationship between the second-order linear equation of motion for the wrist joint and the linear sum of activities of the four wrist prime movers. The symmetric relationship determined a set of parameters to characterize the muscle activities and their similarity to the components of movement kinematics of the wrist joint. We found that muscle activities of the normal controls encoded both the velocity and the position of the moving target, resulting in precise tracking of the target. In contrast, muscle activities of the cerebellar patients were characterized by a severer impairment for velocity control and more dependence on position control, resulting in poor tracking of the smoothly moving target with many step-like awkward movements. Our results suggest that the cerebellum plays an important role in the generation of motor commands for smooth velocity and position control.

An accurate estimate of elapsed time is essential for anticipating the timing of future events. Here, we show that the ability to estimate elapsed time on a reaction time (RT) task improved with training during which human participants learned to anticipate the onset of a “Go” signal. In each trial, a warning signal preceded the Go signal by a temporal interval (i.e., foreperiod). The duration of the foreperiod was randomly drawn from a rectangular distribution (1–2 s). Participants were required to initiate a response immediately after the Go signal and performed the task for 480 trials/day for 12 days. Anticipation should have been governed by the probability that the Go signal would occur (hazard rate), which increased for longer foreperiods. Indeed, RTs decreased for longer foreperiods and were inversely related to the hazard rate. The pattern of RT decrease was well explained by the subjective hazard rate, which was formalized based on the assumption that the uncertainty of estimates of elapsed time scales with time (Weber’s law). Notably, RTs demonstrated a more linear decrease as a function of foreperiod in LATE compared with EARLY training sessions. This involved a decrease in the Weber fraction used in the subjective hazard rate. The results indicate that the uncertainty associated with estimating elapsed time was reduced as participants learned and used the hazard rate to anticipate the onset of the Go signal. This finding suggests that the ability to estimate elapsed time improves with training on behavioral tasks that implicitly engage timing mechanisms.

In this study, we introduce a new method to analyze the functional significance of motor commands based on the causal relationship between muscle activities and movement kinematics. We asked 4 healthy subjects to perform 2 movement tasks involving movements of the wrist joint with a manipulandum: (1) a step-tracking movement, and (2) a smooth pursuit movement to follow a smoothly moving target with a cursor. We recorded the movements of the wrist joint and the electromyography (EMG) signals from 4 prime movers of the wrist. We then identified the causal relationship between the muscle activities and the movement kinematics in terms of the torque at the wrist joint torque. Correlation coefficients (R) between the muscle activities and the movement kinematics were surprisingly high for both the step-tracking movement (0.88-0.96) and the smooth pursuit movement (0.89-0.98). Nevertheless, the ratio of the viscosity coefficient B and the elastic coefficient K for the of the causal relationship was systematically different for the 2 movement tasks. For the step-tracking movement, the elastic coefficient K was much higher than the viscosity coefficient B (KB, B/K ratio = 0-0.25), suggesting that the muscle activities were correlated mainly with position of the wrist joint. In other words, the central nervous system (CNS) mainly controls the target position during the step-tracking movement. In contrast, for the smooth pursuit movement, the elastic coefficient K and the viscosity coefficient B were similar (B approximately equal to K, B/K ratio = 1.0-2.1), suggesting that the muscle activities were correlated both with the position and velocity of the wrist joint. In other words, the CNS controls the velocity as well as position of the target during the smooth pursuit movement. Overall, the controller for the wrist movement can switch between the position-control mode and the position/velocity-control mode depending on the requirement of the task. Our new method is a unique noninvasive tool for the bedside evaluation of the condition of motor controllers in the CNS. Thus, it is useful for finding evidence of neurorehabilitation.

Spinal commissural neurons (CNs) activated di- or trisynaptically by stimulation of ipsilateral vestibular afferents were stained with intraaxonal injection of horseradish peroxidase in the cat upper cervical spinal cord. Stem axons of CNs in lamina VIII or VII, after crossing the midline, had ascending and/or descending main branches that gave off multiple axon collaterals to laminae IX and VIII over a few cervical segments. Terminal boutons appeared to make contact with proximal dendrites and somata of retrogradely-labelled neck motoneurons. Therefore, these CNs were regarded as mediating vestibular afferent input to contralateral neck motoneurons trisynaptically at the shortest.

In this paper, we propose a new method to make a quantitative evaluation for movement disorders. Based on the EMG signals, we analyzed the movement disorders for cerebellar patients at the motor command level. As an experimental task, we asked subjects to perform step-tracking wrist movements with a manipulandum, and simultaneously recorded wrist joint movements and muscle activities of four wrist prime movers with surface electrodes. In order to quantitatively evaluate the correspondence between the movement kinematics and the activities of the four muscles, we approximated the relationship between the wrist joint torque calculated from the kinematics and the four EMG signals using a dynamics model of wrist joint. Our surprising observation was that there was very high correlation between the wrist joint torque and the EMG signals. In fact, we identified causal abnormality of muscle activities for movement disorders of cerebellar patients, confirming effectiveness of our proposed method for analysis of movement disorders at the level of the motor command.

In this paper, we propose a new method to make a quantitative evaluation of motor commands based on the EMG signals. Especially, we tried to resolve a remaining issue in our previous study: relatively poor estimation of the wrist joint torque from the EMG signals for extreme movements, such as jerky movements of the cerebellar patients. Subjects included eight cerebellar patients and eight normal controls. As an experimental task, we asked the subjects to perform step-tracking wrist movements with a manipulandum, and recorded movements of the wrist joint and activities of the four wrist prime movers with surface electrodes. For improved estimation of the wrist joint torque from the EMG signals, we developed a new approximating method, by considering the moment arms of the four muscles during the movement. As a result, our improved method proved higher correlations between the kinematics torque and the estimated torque with the four EMG signals for both the cerebellar patients and the normal controls than the previous method. In fact, we confirmed the effectiveness of our improved methods, identifying the causal abnormality of muscle activities for the cerebellar ataxia with high accuracy.

Which brain sites represent the final form of motor commands that encode temporal patterns of muscle activities? Here, we show the possible brain sites which have activity equivalent to the motor commands with functional magnetic resonance imaging (fMRI). We hypothesized that short-temporal patterns of movements or stimuli are reflected in blood-oxygenation-level-dependent (BOLD) responses and we searched for regions representing the response. Participants performed two temporal patterns of tapping and/or listened to the same patterns of auditory stimuli in a 3T fMRI. The patterns were designed to have the same number (11) of events and the same duration, but different temporal distribution of events. The 11 events were divided into two parts (10 repetitive taps and one stand-alone tap) and the interval of the two parts was 3 s. The two patterns had reverse order of the two parts. The results revealed that different temporal patterns of auditory stimuli were represented in different temporal features of BOLD responses in the bilateral auditory cortex, whereas different temporal patterns of tapping were reflected in contralateral primary motor cortex and the ipsilateral anterior cerebellum. In bilateral premotor cortex, supplementary motor area, visual cortex, and posterior cerebellum, task-related BOLD responses were exhibited, but their responses did not reflect the temporal patterns of the movement and/or stimuli. One possible explanation is that the neuronal activities were similar for the two patterns in these regions. The sensitivity of the BOLD response to the temporal patterns reflects local differences in functional contributions to the tasks. The present experimental design and analysis may be useful to reveal particular brain regions that participate in multiple functions.

Anterograde labelling following focal injections of Phaseolus vulgaris leucoagglutinin was used to identify the parietal distribution of thalamocortical (TC) fibers from the ventroanterior-ventrolateral (VA-VL) complex of the cat thalamus. In injections in the ventrolateral or the caudal part of the VA-VL complex, labelled TC fibers were distributed in layers I, III and IV of the parietal areas 5a and/or 5b, whereas in injections located more rostrally or dorsomedially, labelled TC fibers were almost confined to layer I.

In this study, we developed a new system for quantitative evaluation of the wrist movement. We designed this system to analyze the causal relationship between movement disorders and abnormal muscle activities. In addition, this system was also designed to be non-invasive and used handily at the bedside. We tested this system for analysis of movement disorders in the cerebellar patients. As an experimental task, we asked subjects to perform step-tracking wrist movements with a manipulandum, and simultaneously recorded wrist joint movements and muscle activities of four wrist prime movers with surface electrodes. The participants included eight patients with cerebellar diseases and eight normal controls. First, we made quantitative analysis of movement kinematics in the cerebellar patients in terms of accuracy and directional deviation of wrist movements. Then we examined how well the wrist movement could be explained with the activities of the four prime movers. Specifically, we compared the wrist joint torque calculated from the movement of the wrist (kinematic torque) and the wrist joint torque estimated from the muscle activities (muscle torque). Then we evaluated match between the two. Our surprising observation was that there were very high correlations between the kinematic torque and the muscle torque for both normal controls and cerebellar patients. Correlation coefficients R for normal controls were 0.85 +/- 0.06 for X-axis component and 0.78 +/- 0.09 for Y-axis component. On the other hand, correlation coefficients R for cerebellar patients were 0.78 +/- 0.11 for X-axis component and 0.78 +/- 0.1 for Y-axis component. These results strongly suggested that there were enough information in the activities of the four muscles to explain the position, speed and acceleration of the wrist joint. In other words, with our system, it is possible to identify causal abnormality of muscle activities for movement disorders. Therefore, it is possible with our system to analyze movement disorders at a motor command level.

Anticipating the timing of behaviorally relevant events is crucial for organizing movement. The time to initiate actions based on events (i.e., reaction time (RT)) is a useful measure to quantify states of anticipation. Few studies have examined how anticipation affects the timing of limb movements. We addressed this question behaviorally with two macaque monkeys performing delayed wrist movement tasks. The interval between target onset and go signal (i.e., foreperiod) varied randomly from 1 to 2 s. The probability that the go signal was about to occur (i.e., hazard rate) increased as the foreperiod increased. The kinematics of wrist movements was not influenced by foreperiod duration. Analyzing RT data with the LATER model indicated that RT distributions swiveled on reciprobit plots as foreperiods increased, suggesting that changes in RT distributions were due to changes in anticipation. RT was inversely related to hazard rate. To better understand the general implications of anticipatory states, we introduced an additional rectangular foreperiod distribution that ranged from 0.9 to 1.5 s. For that distribution, the hazard rate peaks were higher than those of the 1-2 s distribution. Changes in RT were clearly explained by quantitative differences in hazard rate. The decrease in RT in the 0.9-1.5 s foreperiod distribution was greater than that in the 1-2 s foreperiod. Thus, monkeys learned the temporal structure of foreperiod distributions and anticipated the onset of the go signal, based on hazard rates.

Quantitative evaluation of motor functions of patients with cerebellar ataxia is vital for evidence-based treatments and has been a focus in previous investigations of movement kinematics. Due to redundancy of the musculoskeletal system, muscle activities contain more information than the movement kinematics. Therefore, it is preferable to analyze causal anomalies of muscle activities to evaluate motor functions in patients. Here we propose a new method to evaluate the motor functions at the level of muscle activities and movement kinematics. Nineteen patients and 10 control subjects performed two movement tasks of the wrist joint, a step-tracking task and a pursuit task, with a manipulandum. The movements of the wrist joint and activities of the four wrist prime movers were recorded. We developed a linear model for the wrist joint to approximate the causal relationship between muscle activities and movement kinematics in terms of the wrist joint torque. We used a canonical correlation analysis to verify the causality between the muscle activities and the movement kinematics in the model. We found that the activities of the four muscles were related almost entirely to the position and velocity, with negligible correlation with the acceleration of the wrist joint. Moreover, the ratio of the weights for position- and velocity-related torque components characterized the contents of the muscle activities in terms of the movement kinematics. Next, we compared the ratios for the two movement tasks between the controls and patients. In control subjects, the ratios indicated clear task-specific changes that conformed to the functional requirements of the tasks. In contrast, in patients, the task-specific changes diminished highly significantly. The present results indicate that this ability to accommodate motor commands to the task requirements provides a novel quantitative parameter to characterize motor functions in patients with cerebellar ataxia.

In this chapter, we describe our recent work on the divergent properties of single, long descending motor-tract neurons in the spinal cord, using the method of intra-axonal staining with horseradish peroxidase, and serial-section, three-dimensional reconstruction of their axonal trajectories. This work provides evidence that single motor-tract neurons are implicated in the neural implementation of functional synergies for head movements. Our results further show that single medial vestibulospinal tract (MVST) neurons innervate a functional set of multiple neck muscles, and thereby implement a canal-dependent, head-movement synergy. Additionally, both single MVST and reticulospinal axons may have similar innervation patterns for neck muscles, and thereby control the same functional sets of neck muscles. In order to stabilize redundant control systems in which many muscles generate force across several joints, the CNS routinely uses a combination of a control hierarchy and sensory feedback. In addition, in the head-movement system, the elaboration of functional synergies among neck muscles is another strategy, because it helps to decrease the degrees of freedom in this particularly complicated control system.

In this chapter, we describe our recent work on the divergent properties of single, long descending motor-tract neurons in the spinal cord, using the method of intra-axonal staining with horseradish peroxidase, and serial-section, three-dimensional reconstruction of their axonal trajectories. This work provides evidence that single motor-tract neurons are implicated in the neural implementation of functional synergies for head movements. Our results further show that single medial vestibulospinal tract (MVST) neurons innervate a functional set of multiple neck muscles, and thereby implement a canal-dependent, head-movement synergy. Additionally, both single MVST and reticulospinal axons may have similar innervation patterns for neck muscles, and thereby control the same functional sets of neck muscles. In order to stabilize redundant control systems in which many muscles generate force across several joints, the CNS routinely uses a combination of a control hierarchy and sensory feedback. In addition, in the head-movement system, the elaboration of functional synergies among neck muscles is another strategy, because it helps to decrease the degrees of freedom in this particularly complicated control system.

We investigated the axonal morphology of single corticothalamic (CT) neurons of the motor cortex (Mx) in the cat thalamus, using a neuronal tracer, biotinylated dextran amine (BDA). After localized injection of BDA into the Mx, labeled CT axons were found ipsilaterally in the thalamic reticular nucleus (TRN), the ventroanterior–ventrolateral complex (VA-VL), the central lateral nucleus (CL), the central medial nucleus, and the centromedian nucleus, but with the primary focus in the VA-VL. The terminals in the VA-VL formed a large laminar cluster, which extended approximately in parallel with the internal medullary lamina. The laminar organization mirrored morphologic features of single CT axons. We reconstructed the trajectories of 25 single CT axons that arose from layer V (16 axons) or layer VI (9 axons) and terminated in the VA-VL. Terminals of single CT axons that originated from both layer V and layer VI were confined within a laminar structure about 700 μm thick, suggesting the existence of laminar input organization in the VA-VL. Otherwise, the two groups of the CT axons showed contrasting features. All of the CT axons derived from layer VI gave rise to a few short collaterals to the TRN and then formed extensive arborization with numerous small, drumstick-like terminals in the VA-VL. On the other hand, the CT axons arising from layer V gave rise to collaterals whose main axons descended into the cerebral peduncle. Each collateral projected to the VA-VL or CL without projection to the TRN and formed a few small clusters of giant terminals. The two groups of CT neurons in the same cortical column had convergent rather than segregated termination in the VA-VL. However, the terminals of layer VI CT neurons were distributed diffusely and widely in the VA-VL, whereas the terminals of layer V CT neurons were much more focused and surrounded by the terminals of the former group. These contrasting features of the two types of CT projections appear to represent their different functional roles in the generation of motor commands and control of movements in the Mx. J. Comp. Neurol. 437:170–185, 2001. © 2001 Wiley-Liss, Inc.

What aspects of movement are represented in the primary motor cortex (M1): relatively low-level parameters like muscle force, or more abstract parameters like handpath? To examine this issue, the activity of neurons in M1 was recorded in a monkey trained to perform a task that dissociates three major variables of wrist movement: muscle activity, direction of movement at the wrist joint, and direction of movement in space. A substantial group of neurons in M1 (28 out of 88) displayed changes in activity that were muscle-like. Unexpectedly, an even larger group of neurons in M1 (44 out of 88) displayed changes in activity that were related to the direction of wrist movement in space independent of the pattern of muscle activity that generated the movement. Thus, both “muscles” and “movements” appear to be strongly represented in M1.

To investigate whether corticothalamic (CT) neurons in the motor cortex (Mx) receive cerebellar input via the ventroanterior–ventrolateral nucleus of the thalamus (VA–VL), we recorded intracellular potentials from neurons in the Mx of anesthetized cats and examined effects of stimulation of the VA–VL and the brachium conjunctivum on them. After this electrophysiological identification, horseradish peroxide (HRP) was injected iontophoretically into the recorded neurons for morphological analysis. We identified 34 neurons as CT neurons by their antidromic response to stimulation of the VA–VL, of which 13 were layer VI CT neurons and 21 were layer V CT neurons. A majority of the CT neurons of both layers VI and V received monosynaptic excitatory postsynaptic potentials (EPSPs) from the VA–VL and di- or polysynaptic EPSPs from the cerebellum. The laminar distribution and morphological characteristics of single CT neurons receiving cerebellar input were analyzed on 19 HRP-labeled CT neurons. Eight layer V and six layer VI CT neurons were reconstructed from serial sections. All the reconstructed layer VI CT neurons were modified pyramidal neurons whose apical dendrites ended in layer III or V, and all the stained layer V CT neurons were typical pyramidal neurons, although the laminar and tangential distribution of recurrent collaterals of these neurons varied from neuron to neuron.

This study was performed to investigate the pattern of input and the pathways from the six semicircular canals to motoneurons of various neck muscles in anesthetized cats. Intracellular postsynaptic potentials from neck motoneurons were recorded in response to electrical stimulation of the six ampullary nerves. The results showed that motoneurons of a particular neck muscle have a homogeneous convergent pattern of input from the six semicircular canals; there are four patterns of input from the six semicircular canals to motoneurons of various neck muscles; and the trisynaptic connection between the semicircular canal nerves and neck motoneurons was identified in addition to the disynaptic connection.

Axons of reticulospinal neurons (RSNs) activated monosynaptically by stimulation of the contralateral superior colliculus (SC) were stained with intraaxonal injection of horseradish peroxidase in the cat upper cervical spinal cord. Stem axons of single RSNs gave rise to multiple axon collaterals to laminae IX, VIII and VII over a few cervical segments. Single RSNs made contacts with retrogradely labeled neck motoneurons of different neck muscles. Therefore, RSNs were regarded as mediating output of the SC to functionally different groups of neck muscles simultaneously. The result gave evidence of neural implementation of a functional synergy for a neck movement at a single neuron level.

Publisher Summary This chapter reviews long descending motor tract systems controlling axial and limb muscles, including motoneurons and interneurons. It also describes the morphological properties of single long descending motor tract axons in the lateral and the medial descending motor systems. Single long descending motor tract axons are not a simple private line connecting supraspinal centers and motoneurons, but they may exert influences onto different groups of spinal neurons simultaneously at widely separated segments with their multiple axon collaterals. The long descending motor tracts, and their target motor nuclei, and interneurons may be principally segregated into the medial and lateral motor systems. The medial system is phylogenetically and ontogenetically older than the lateral system. It characteristically steers body and integrated limb and body movements, and movement synergisms of individual limbs involving various parts.

In the cat, the cerebellum projects via the ventroanterior-ventrolateral (VA-VL) complex of the thalamus to the motor and premotor cortices and also to the parietal association cortex. Cerebellar inputs to each of these regions have been characterized electrophysiologically by depth profiles of cortical potentials following stimulation of the brachium conjunctivum and of the VA-VL complex, and morphologically by the laminar distribution of thalamocortical (TC) terminations, in aggregate and at the single-axon level. One population of TC neurons terminated mainly in layer I and was associated with late surface negative potentials. A second population, with terminations in layers III and IV, was associated with early deep negative potentials. Terminations in layer III of the motor cortex formed multiple patches about 1-1.5 mm wide (mediolateral), which aligned to form 2-5 mm stripes extended rostrocaudally. This pattern correlates with the configuration of individual TC axons, which have two to six separate terminal patches distributed over 6 mm (rostrocaudal). The wide morphological divergence of single TC axons in the cortex may imply functionally multiple innervation of different efferent columns. Alternately, along with other inputs, it may permit a highly dynamic output selection from multiple representations, for example, of a variety of muscle groups in different combinations.

Publisher Summary This chapter discusses intracellular recording to determine the projections of interpositus (IN) or the dentate (DN) to single thalamocortical neurons (TCNs) in ventrolateral nucleus of the thalamus (VL). To get detailed morphological information about the input-output organization of the VL, intracellular HRP staining of single cerebellothalamic afferents and thalamocortical axons is performed. To examine inputs from IN and DN to single TCNs in VL, intracellular recordings are made from 430 TCNs that are identified by their antidromic responses to stimulation of the pericruciate cortex in the cat. To investigate the proportion of VL neurons that receive inputs from both IN and DN and the relative strengths of these inputs to neurons in different parts of VL, VL is systematically explored latero-medially at 300μm intervals in the same transverse plane with the same recording micropipette throughout the experiment. The results showed that both IN and DN projected to a wide area of VL and the respective projection areas overlapped each other considerably. But there is a general tendency that DN projected more abundantly to the medial portion of VL, whereas IN projected more laterally than DN.

Input-output organization of the ventrolateral nucleus (VL) of the thalamus was analyzed electrophysiologically and morphologically at the single cell level. Virtually all pyramidal tract neurons in the motor cortex and area 6 received convergent inputs from the dentate (DN) and the interpositus (IN) nuclei and about 60% of thalamocortical (TC) neurons received convergent inputs from both the DN and the IN. Anterograde labelling following focal injection of Phaseolus vulgaris leukoagglutinin and intracellular staining of TC axons showed that the terminals in layer III tended to aggregate into patches about 1-1.5 mm wide in a frontal plane, which were arranged in longitudinal strips about 2-5 mm long in a rostrocaudal direction.

The characteristics of cerebellar input to the parietal cortex through the ventroanterior-ventrolateral (VA-VL) complex of the thalamus were investigated in the adult cat by using combined electrophysiological and anatomical methods. Two distinct parietal regions were activated by stimulation of the cerebellar nuclei (CN). In the first region located in the depth of the bank of the ansate sulcus, stimulation of the CN induced early surface positive-deep negative potentials and late surface negative-deep positive potentials. In this cortical area, potentials of similar shape and time course were evoked at a shorter latency by stimulation of the ventrolateral part of the VA-VL complex where large negative field potentials were evoked by stimulation of the CN. After injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in this part of the VA-VL complex, axon terminals of thalamocortical (TC) fibers were found in layers I, III and IV in the depth of the bank of the ansate sulcus and layers I and III in the motor cortex. In the second region located in the suprasylvian gyrus, late surface negative-deep positive potentials were evoked by stimulation of the CN and similar potentials were evoked at a shorter latency from the dorsomedial part of the VA-VL complex where large cerebellar-evoked potentials could be recorded. PHA-L injection in this thalamic region stained TC fibers and their terminals in layer I of the suprasylvian gyrus, and in layers I and III of the motor cortex. The laminar distribution of TC axon terminals in two different regions of the parietal cortex could account for the depth profiles of the cerebellar- and the thalamic-evoked potentials in each region. These results show that cerebellar information is conveyed to two separate areas in the parietal cortex by two different TC pathways.