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Background Cerebral small vessel disease is associated with higher ratios of soluble-epoxide hydrolase derived linoleic acid diols (12,13-dihydroxyoctadecenoic acid [DiHOME] and 9,10-DiHOME) to their parent epoxides (12(13)-epoxyoctadecenoic acid [EpOME] and 9(10)-EpOME); however, the relationship has not yet been examined in stroke. Methods and Results Participants with mild to moderate small vessel stroke or large vessel stroke were selected based on clinical and imaging criteria. Metabolites were quantified by ultra-high-performance liquid chromatography-mass spectrometry. Volumes of stroke, lacunes, white matter hyperintensities, magnetic resonance imaging visible perivascular spaces, and free water diffusion were quantified from structural and diffusion magnetic resonance imaging (3 Tesla). Adjusted linear regression models were used for analysis. Compared with participants with large vessel stroke (n=30), participants with small vessel stroke (n=50) had a higher 12,13-DiHOME/12(13)-EpOME ratio (β=0.251, P=0.023). The 12,13-DiHOME/12(13)-EpOME ratio was associated with more lacunes (β=0.266, P=0.028) but not with large vessel stroke volumes. Ratios of 12,13-DiHOME/12(13)-EpOME and 9,10-DiHOME/9(10)-EpOME were associated with greater volumes of white matter hyperintensities (β=0.364, P

Fixational eye movements ( FEMs), including microsaccades, drift, and tremor, shift our eye position during ocular fixation, producing retinal motion that is thought to help visibility by counteracting neural adaptation to unchanging stimulation. Yet, how each FEM type influences this process is still debated. Recent studies found little to no relationship between microsaccades and visual perception of spatial frequencies ( SF). However, these conclusions were based on coarse analyses that make it hard to appreciate the actual effects of microsaccades on target visibility as a function of SF. Thus, how microsaccades contribute to the visibility of stimuli of different SFs remains unclear. Here, we asked how the visibility of targets of various SFs changed over time, in relationship with concurrent microsaccade production. Participants continuously reported on changes in target visibility, allowing us to time-lock ongoing changes in microsaccade parameters to perceptual transitions in visibility. Microsaccades restored/increased the visibility of low SF targets more efficiently than that of high SF targets. Yet, microsaccade rates rose before periods of increased visibility, and dropped before periods of diminished visibility, for all the SFs tested, suggesting that microsaccades boosted target visibility across a wide range of SFs. Our data also indicate that visual stimuli fade/become harder to see less often in the presence of microsaccades. In addition, larger microsaccades restored/increased target visibility more effectively than smaller microsaccades. These combined results support the proposal that microsaccades enhance visibility across a broad variety of SFs. [ABSTRACT FROM AUTHOR]

Songbirds possess acute vision. How higher brain centres represent basic and parameterised visual stimuli to process sensory signals according to their behavioural importance has not been studied in a systematic way. We therefore examined how carrion crows ( Corvus corone) and their nidopallial visual neurons process global visual motion information in dynamic random-dot displays during a delayed match-to-sample ( DMS) task. The behavioural data show that moderately fast motion speeds (16° of visual angle/s) result in superior direction discrimination performance. To characterise how neurons encode and maintain task-relevant visual motion information, we recorded the single-unit activity in the telencephalic association area 'nidopallium caudolaterale' ( NCL) of behaving crows. The NCL is considered to be the avian analogue of the mammalian prefrontal cortex. Almost a third (28%) of randomly selected NCL neurons responded selectively to the motion direction of the sample stimulus, mostly to downward motions. Only few NCL neurons (7.5%) responded consistently to specific motion directions during the delay period. In error trials, when the crows chose the wrong motion direction, the encoding of motion direction was significantly reduced. This indicates that sensory representations of NCL neurons are relevant to the birds' behaviour. These data suggest that the corvid NCL, even though operating at the apex of the telencephalic processing hierarchy, constitutes a telencephalic site for global motion integration. [ABSTRACT FROM AUTHOR]

Several experiments have shown that smooth pursuit and saccades interact while tracking an object moving across the visual scene. It was proposed two decades ago that the amplitude of saccades triggered during smooth pursuit ('catch-up saccades') were corrected by a delayed sensory signal to account for the ongoing target displacement during catch-up saccades. However, recent studies used targets with non-constant velocity profiles and suggested that the correction of catch-up saccade amplitude must be done through an internal model of target motion. It is widely accepted that an internal model of target motion is also used by the central nervous system (CNS) to cancel inherent delays between visual input and smooth pursuit motor output, ensuring accurate tracking of moving targets. Our study proposes a new paradigm in which the target switches unexpectedly from one target with a non-constant periodic velocity profile to another with a non-constant aperiodic velocity profile. Our results confirm the hypothesis that the CNS uses an internal model of target motion to correct catch-up saccade amplitude. In addition, we reconcile the sensory delayed and the internal model of target motion hypotheses and show that a common internal model of target motion is shared within the CNS to control smooth pursuit and to correct catch-up saccade amplitude. [ABSTRACT FROM AUTHOR]

The superior colliculus ( SC) plays a key role in controlling spatial attention. It is hypothesized that some forms of spatial attention, such as the detection of a single salient object arise from lateral competitive interactions between different locations within the spatial map in the SC. This hypothesis is supported by a recent in vitro study showing that a 'Mexican hat'-like pattern of synaptic connectivity is implemented in the intrinsic circuit of the superficial layer of the SC ( sSC). However, the neuronal population mechanisms responsible for this pattern still remain unclear. Here, we examined how spatial response modulations, for example lateral interactions and surround suppression, are represented at the neuronal population level using in vivo two-photon calcium imaging in the mouse sSC. Observation of neuronal population responses with single-cell resolution enabled us to identify a small subset of neurons that were activated by relatively small visual stimuli (< 1° diameter), and thus allowed us to detect the exact location of the 'response center' in the sSC to a visual stimulus presented at a given location. We demonstrated that presenting two-point stimuli or one large stimulus modulated the spatial response pattern of the neuronal population, i.e. centre facilitation and surround suppression. Furthermore, we found that both GABAergic and non- GABAergic neurons showed a similar population response pattern of surround suppression. The population dynamics suggest the circuit mechanism underlying lateral inhibition and surround suppression may be supported by long-range inhibitory neurons in the sSC. [ABSTRACT FROM AUTHOR]

Ocular following responses (OFRs) are elicited at ultra-short latencies (< 60 ms) by sudden movements of the visual scene. In this study, we investigated the roles of color signals in OFRs in monkeys. To make physiologically isoluminant sinusoidal color gratings, we estimated the physiologically isoluminant points using OFRs and found that the physiologically isoluminant points were nearly independent of the spatiotemporal frequency of the gratings. We recorded OFRs induced by the motion of physiologically isoluminant color gratings and found that OFRs elicited by the motion of color gratings had different spatiotemporal frequency tuning from those elicited by the motion of luminance gratings. Additionally, OFRs to isoluminant color gratings had smaller peak responses, suggesting that color signals weakly contribute to OFRs compared with luminance signals. OFRs to the motion of stimuli composed of luminance and color signals were also examined. We found that color signals largely contributed to OFRs under low luminance signals regardless of whether color signals moved in the same or opposite direction to luminance signals. These results provide evidence of the multichannel visual computations underlying motor responses. We conclude that, in everyday situations, color information contributes cooperatively with luminance information to the generation of ocular tracking behaviors. [ABSTRACT FROM AUTHOR]

Although a direct relationship between numerical allocation and spatial attention has been proposed, recent research suggests that these processes are not directly coupled. In keeping with this, spatial attention shifts induced either via visual or vestibular motion can modulate numerical allocation in some circumstances but not in others. In addition to shifting spatial attention, visual or vestibular motion paradigms also (i) elicit compensatory eye movements which themselves can influence numerical processing and (ii) alter the perceptual state of 'self', inducing changes in bodily self-consciousness impacting upon cognitive mechanisms. Thus, the precise mechanism by which motion modulates numerical allocation remains unknown. We sought to investigate the influence that different perceptual experiences of motion have upon numerical magnitude allocation while controlling for both eye movements and task-related effects. We first used optokinetic visual motion stimulation ( OKS) to elicit the perceptual experience of either ' visual world' or ' self'-motion during which eye movements were identical. In a second experiment, we used a vestibular protocol examining the effects of perceived and subliminal angular rotations in darkness, which also provoked identical eye movements. We observed that during the perceptual experience of ' visual world' motion, rightward OKS-biased judgments towards smaller numbers, whereas leftward OKS-biased judgments towards larger numbers. During the perceptual experience of ' self-motion', judgments were biased towards larger numbers irrespective of the OKS direction. Contrastingly, vestibular motion perception was found not to modulate numerical magnitude allocation, nor was there any differential modulation when comparing ' perceived' vs. ' subliminal' rotations. We provide a novel demonstration that numerical magnitude allocation can be differentially modulated by the perceptual state of self during visual but not vestibular mediated motion. [ABSTRACT FROM AUTHOR]

Adaptation to changing environmental demands is central to maintaining optimal motor system function. Current theories suggest that adaptation in both the skeletal-motor and oculomotor systems involves a combination of fast (reflexive) and slow (recalibration) mechanisms. Here we used the oculomotor vergence system as a model to investigate the mechanisms underlying slow motor adaptation. Unlike reaching with the upper limbs, vergence is less susceptible to changes in cognitive strategy that can affect the behaviour of motor adaptation. We tested the hypothesis that mechanisms of slow motor adaptation reflect early neural processing by assessing the linearity of adaptive responses over a large range of stimuli. Using varied disparity stimuli in conflict with accommodation, the slow adaptation of tonic vergence was found to exhibit a linear response whereby the rate ( R2 = 0.85, P < 0.0001) and amplitude ( R2 = 0.65, P < 0.0001) of the adaptive effects increased proportionally with stimulus amplitude. These results suggest that this slow adaptive mechanism is an early neural process, implying a fundamental physiological nature that is potentially dominated by subcortical and cerebellar substrates. [ABSTRACT FROM AUTHOR]

The dorsal premotor cortex residing in the dorsolateral aspect of area 6 is a rostrocaudally elongated area that is rostral to the primary motor cortex (M1) and caudal to the prefrontal cortex. This region, which is subdivided into rostral [pre-dorsal premotor cortex (pre- PMd)] and caudal [dorsal premotor cortex proper (PMd)] components, probably plays a central role in planning and executing actions to achieve a behavioural goal. In the present study, we investigated the functional specializations of the pre- PMd, PMd, and M1, because the synthesis of the specific functions performed by each area is considered to be essential. Neurons were recorded while monkeys performed a conditional visuo-goal task designed to include separate processes for determining a behavioural goal (reaching towards a right or left potential target) on the basis of visual object instructions, specifying actions (direction of reaching) to be performed on the basis of the goal, and preparing and executing the action. Neurons in the pre- PMd and PMd retrieved and maintained behavioural goals without encoding the visual features of the visual object instructions, and subsequently specified the actions by multiplexing the goals with the locations of the targets. Furthermore, PMd and M1 neurons played a major role in representing the action during movement preparation and execution, whereas the contribution of the pre- PMd progressively decreased as the time of the actual execution of the movement approached. These findings revealed that the multiple processing stages necessary for the realization of an action to accomplish a goal were implemented in an area-specific manner across a functional gradient from the pre- PMd to M1 that included the PMd as an intermediary. [ABSTRACT FROM AUTHOR]

Chronic nerve injuries are notorious for their poor regenerative outcomes. Here, we addressed the question of whether the established reduced ability of injured motoneurons to regenerate their axons with time of disconnection with targets (chronic axotomy) is associated with a failure of injured motoneurons to express and sustain their expression of regeneration-associated genes. Sciatic motoneurons were prevented from regenerating by ligation of the transected nerves (chronic axotomy), and then subjected to a second nerve transection (acute axotomy) to mimic the clinical surgical procedure of refreshing the proximal nerve stump prior to delayed nerve repair. The expression of α1-tubulin, actin and GAP-43 mRNA was analysed in axotomized sciatic motoneurons by the use of in situ hybridization followed by autoradiography and silver grain quantification. The expression of these regeneration-associated genes by naive (acutely) axotomized motoneurons declined exponentially, to reach baseline levels within 6 months. These chronically injured motoneurons responded to a refreshment axotomy by elevating the expression of the genes to the same levels as in acutely (i.e. for the first time) axotomized sciatic motoneurons. However, the expression of these declined more rapidly than after acute axotomy. We conclude that a progressive decline in the expression of the regeneration-associated genes in chronically axotomized motoneurons and the even more rapid decline in their expression in response to a refreshment axotomy may explain why the regenerative capacity of chronically axotomized neurons declines with time. [ABSTRACT FROM AUTHOR]