Добірка наукової літератури з теми "Lateral occipital cortex"

Object. The lateral occipital cortex in humans is known as the “extrastriate visual cortex.” It is, however, an unexplored field of research, and the anatomical nomenclature for its surface has still not been standardized. This study was designed to investigate whether the lateral occipital cortex in humans has retinotopic representation. Methods. Four right-handed patients with a diagnosis of intractable epilepsy from space-occupying lesions in the occipital lobe or epilepsy originating in the occipital lobe received permanently implanted subdural electrodes. Electrical cortical stimulation was applied directly applied to the brain through metal electrodes by using a biphasic stimulator. The location of each electrode was measured on a lateral skull x-ray study. Each patient considered a whiteboard with vertical and horizontal median lines. The patient was asked to look at the midpoint on the whiteboard. If a visual hallucination or illusion occurred, the patient recorded its outline, shape, color, location, and motion on white paper one tenth the size of, and with vertical and horizontal median lines similar to those on, the whiteboard. Polar angles and eccentricities of the midpoints of the phosphenes from the coordinate origin were measured on the paper. On stimulation of the lateral occipital lobe, 44 phosphenes occurred. All phosphenes were circular or dotted, with a diameter of approximately 1 cm, except one that was like a curtain in the peripheral end of the upper and lower visual fields on stimulation of the parietooccipital region. All phosphenes appeared in the visual field contralateral to the cerebral hemisphere stimulated. On stimulation of the lateral occipital lobe, 22 phosphenes moved centrifugally or toward a horizontal line. From three-dimensional scatterplots and contour maps of the polar angles and eccentricities in relation to the x-ray coordinates of the electrodes, one can infer that the lateral occipital cortex in humans has retinotopic representation. Conclusions. The authors found that phosphenes induced by electrical cortical stimulation of the lateral occipital cortex represent retinotopy. From these results one can assert that visual field representation with retinotopic relation exists in the extrastriate visual cortex.

Previous functional magnetic resonance imaging (MRI) found various brain areas in the temporal and occipital lobe involved in integrating auditory and visual object information. Fiber tracking based on diffusion-weighted MRI suggested neuroanatomical connections between auditory cortex and sub-regions of the temporal and occipital lobe. However, the relationship between functional activity and white-matter tracks remained unclear. Here, we combined probabilistic tracking and functional MRI in order to reveal the structural connections related to auditory–visual object perception. Ten healthy people were examined by diffusion-weighted and functional MRI. During functional examinations they viewed either movies of lip or body movements, listened to corresponding sounds (phonological sounds or body action sounds), or a combination of both. We found that phonological sounds elicited stronger activity in the lateral superior temporal gyrus (STG) than body action sounds. Body movements elicited stronger activity in the lateral occipital cortex than lip movements. Functional activity in the phonological STG region and the lateral occipital body area were mutually modulated (sub-additive) by combined auditory–visual stimulation. Moreover, bimodal stimuli engaged a region in the posterior superior temporal sulcus (STS). Probabilistic tracking revealed white-matter tracks between the auditory cortex and sub-regions of the STS (anterior and posterior) and occipital cortex. The posterior STS region was also found to be relevant for auditory–visual object perception. The anterior STS region showed connections to the phonological STG area and to the lateral occipital body area. Our findings suggest that multisensory networks in the temporal lobe are best revealed by combining functional and structural measures.

The occipito-temporal cortex is strongly implicated in carrying out the high-level computations associated with vision. In human neuroimaging studies, focal regions are consistently found within this broad region that respond strongly and selectively to faces, bodies, or objects. A notable feature of these selective regions is that they are found in pairs. In the posterior-lateral occipito-temporal cortex, focal selectivity is found for faces (occipital face area), bodies (extrastriate body area), and objects (lateral occipital). These three areas are found bilaterally and at close quarters to each other. Likewise, in the ventro-medial occipito-temporal cortex, three similar category-selective regions are found, also in proximity to each other: for faces (fusiform face area), bodies (fusiform body area), and objects (posterior fusiform). Here we review some of the extensive evidence on the functional properties of these areas with two aims. First, we seek to identify principles that distinguish the posterior-lateral and ventro-medial clusters of selective regions but that apply generally within each cluster across the three stimulus kinds. Our review identifies and elaborates several principles by which these relationships hold. In brief, the posterior-lateral representations are more primitive, local, and stimulus-driven relative to the ventro-medial representations, which in contrast are more invariant to visual features, global, and linked to the subjective percept. Second, because the evidence base of studies that compare both posterior-lateral and ventro-medial representations of faces, bodies, and objects is still relatively small, we seek to provoke more cross-talk among the research strands that are traditionally separate. We identify several promising approaches for such future work.

To recognize an action, an observer exploits information about the applied manipulation, the involved objects, and the context where the action occurs. Context, object, and manipulation information are hence expected to be tightly coupled in a triadic relationship (the COM triad hereafter). The current fMRI study investigated the hemodynamic signatures of reciprocal modulation in the COM triad. Participants watched short video clips of pantomime actions, that is, actions performed with inappropriate objects, taking place at compatible or incompatible contexts. The usage of pantomime actions enabled the disentanglement of the neural substrates of context–manipulation (CM) and context–object (CO) associations. There were trials in which (1) both manipulation and objects, (2) only manipulation, (3) only objects, or (4) neither manipulation nor objects were compatible with the context. CM compatibility effects were found in an action-related network comprising ventral premotor cortex, SMA, left anterior intraparietal sulcus, and bilateral occipito-temporal cortex. Conversely, CO compatibility effects were found bilaterally in lateral occipital complex. These effects interacted in subregions of the lateral occipital complex. An overlap of CM and CO effects was observed in the occipito-temporal cortex and the dorsal attention network, that is, superior frontal sulcus/dorsal premotor cortex and superior parietal lobe. Results indicate that contextual information is integrated into the analysis of actions. Manipulation and object information is linked by contextual associations as a function of co-occurrence in specific contexts. Activation of either CM or CO associations shifts attention to either action- or object-related relevant information.

There are two predominant means of identifying visual areas in the human brain; retinotopy (exploiting maps of the visual field) and localisers (exploiting functional selectivity). This thesis aimed to bridge those two approaches, assessing the roles of LO-1 and LO-2; two retinotopically-defined regions that show overlap with the functionally-defined (shape selective) Lateral Occipital Complex (LOC). More generally, we asked what is the nature of the shape representation across Lateral Occipital cortex? We first probed the functional roles of LO-1 and LO-2, finding that LO-2 is the more shape-sensitive region of the pair and will respond to second order shape stimuli, whereas LO-1 may process more local cues (perhaps orientation information). Our later work then assessed neural shape representations across visual cortex, identifying two discrete representations; ‘Shape-profile’ (essentially retinotopic responses) and ‘Shape-complexity’ (responses based upon the complexity of a shape’s contour). The latter dimension captured variance in LOC, and surprisingly LO-2. This indicates that even explicit visual field maps can respond to non‑retinotopic attributes such as curvature complexity. Intriguingly, a transition between dimensions occurred around LO-1 and LO-2. Finally, we explicitly tested whether the ‘Shape-complexity’ representation may be curvature based. Our results implied that radial shape protrusions are highly salient features for Lateral Occipital cortex, but it is not necessarily the points of maximal curvature that are being responded to. Instead, we hypothesise that it is the convergent lines comorbid with curvature that neurons may be attuned to, as such lines likely represent the most salient or characteristic features in a given shape. In sum, we argue for an evolving shape representation across visual cortex, with some degree of shape sensitivity first emerging around LO-1 and LO-2. These maps may then be acting as preliminary processing stages for more selective shape tunings in LOC.

This thesis aimed to probe the functional specializations present within several retinotopic divisions of human lateral occipital cortex (LO). The divisions of interest were LO1 and LO2, two neighbouring visual field maps that are found within object-selective LO; the posterior portion of a larger area referred to as the lateral occipital complex (LOC), and V5/MT, the well-known visual complex that is highly selective to visual motion. In order to seek out the causal roles played by these divisions in human visual perception, I used transcranial magnetic stimulation to temporarily disrupt neural processing within these areas, while observers performed visual tasks. The visual tasks I employed examined both spatial vision, through orientation and shape discriminations, and motion processing, through speed discrimination. The data revealed a number of double dissociations. A double dissociation was present between LO1 and V5/MT in the perceptions of orientation and speed. A similar pattern of results was present during orientation and speed discrimination of the same moving stimuli, although this effect was markedly weaker. Additionally, a double dissociation was present between LO1 and LO2 in the perceptions of static orientation and shape, respectively. These double dissociations suggest that LO1, LO2 and V5/MT exhibit functional specializations for orientation, shape and speed, respectively and moreover, perform these specialized roles largely independently of one another. It is unsurprising that I found evidence for parallel processing of motion and aspects of spatial processing because: (1) V5/MT has been shown to be a cluster of multiple visual field maps with a common foveal representation – a feature that has led to the idea that the maps within clusters perform related aspects of processing, but are independent of the processing undertaken in adjacent visual field map clusters like LO; (2) neuropsychological evidence, from studies of akinetopsia and visual form agnosia, points to a double dissociation in processing of motion and form and (3) there is evidence of parallel processing pathways from early visual areas and even subcortical structures to V5/MT. The parallel processing of orientation and shape in LO1 and LO2 is a novel and more surprising finding for the following reasons: (1) These visual field maps are adjacent maps within a single cluster and therefore, might be expected to perform a series of related and dependent roles and (2) shape, as defined here by curvature, could be seen as a property that is dependent on orientation processing. These findings therefore, point to an architecture whereby the extrastriate visual maps in LO sample visual information from antecedent visual areas in parallel, to extract higher order spatial statistics. Mutual retinotopic information and parallel processing not only reduces replicated information across maps but also, provides a common mechanism for communication between maps which exhibit different specializations. Importantly, the well-known category-selectivity of extrastriate regions, like LO, may simply emerge from patterns of unique and low-level visual computations, which encode category specific image statistics, performed by the individual visual field maps that subdivide these areas.

Any natural visual environment contains a huge collection of objects, which impact on our perception and compete for drawing our interest and therefore for being preferentially noticed. By effectively selecting a relevant fraction of the incoming information for further in-depth processing, visual selective attention (VSA) optimizes vision in order to overcome the intrinsically limited computational capacity of the visual system. Single-unit recording studies have demonstrated that multiple stimuli simultaneously impinging onto the receptive field (RF) of a given neuron compete for controlling its firing by interacting with each other through mutual inhibition (Reynold & Chelazzi, 2004; Chelazzi et al., 2011; see also Biased competition model by Moran & Desimone, 1985). Thus, neural responses to stimulus pairs in the RF approximate a weighted average of the responses elicited by individual stimuli (for further details, see Reynold & Chelazzi, 2004; Chelazzi et al., 2011; see also Normalization model by Reynolds et al., 1999). The crucial question to ask is how the competition is resolved. Neurophysiological studies have shown that when two stimuli are simultaneously presented within the same receptive field (RF), neuronal responses in the absence of attentional control are largely determined by the strongest or most salient stimulus, e.g. the one presented at higher luminance contrast, which stands conspicuously against the background (Reynolds & Desimone, 2003). This reflects a bottom-up biasing of the competition on the basis of stimulus saliency. Crucially, top-down attentional control can resolve the competition between stimuli in favor of the most behaviorally relevant stimulus (target) by specifying its properties. In other words, attention can switch control of the neuronal response to the stimulus of interest, independently of its saliency, so that the target will determine the response of that neuron; in other words, the response of a given neuron to a pair of stimuli impinging on its RF will equate the neuronal response to the target stimulus, when presented alone. As a consequence, the neuronal representation of the target is enhanced within visual areas at the expense of the visual representation of the distractor (Corbetta et al., 1990; Treue & Trujillo, 1999; Luck et al., 2000, for reviews, see Chelazzi et al., 2011; Carrasco, 2011; Roe et al., 2012). Importantly, there is a wide range of observations which describe the impact of attention on sensory representations along the visual pathway. Crucially, attentional biasing of the neuronal activity within visual cortices is not uniform, but rather results in different forms of neuronal modulation (see e.g. Treue & Martinez Trujillo, 1999; Fries et al., 2001, 2008; Martinez-Trujillo & Treue, 2002; Carrasco et al., 2000; Carrasco, 2006). The traditional view of VSA maintains that attentional control is organized in a master-slave hierarchical manner: Modulatory top-down signals from a distributed frontoparietal attentional network (e.g. Moore, Armstrong, 2003; Wardak et al., 2004; Silvanto et al., 2006) - the master - impact on sensory (visual) cortical areas - the slave. In other words, lower-order sensory areas execute visual representations commanded via feedback projections from higher-order centers. Recent research has greatly challenged this conventional view, leading to the new and striking hypothesis that master centers do not have an exclusive role in attentional control, but rather the slave ventral (and dorsal) visual pathway areas might capitalize on their internal microcircuitry to directly instantiate attentional mechanisms even in the absence of control from master centers (e.g. Reynolds & Heeger, 2009; Baluch & Itti, 2011). Interestingly, a behavioral assessment following circumscribed lesions of macaque areas V4 and TEO showed a strong impairment in the animal ability to select a stimulus based on its behavioral relevance while discarding other, perceptually more conspicuous stimuli; in other word, after lesions to those areas, the behavior of the animal was at the mercy of stimulus salience (De Weerd et al., 1999; see also Gallant et al., 2000 for analogous findings in humans). These areas along the ventral pathway have therefore been claimed as essential for the instantiation of attentional mechanisms, and in particular mechanisms for the efficient filtering of non-relevant distractors (De Weerd et al., 1999; Chelazzi et al., 2011). The aim of the present study is to extend the current understanding of the brain mechanisms underlying VSA, by directly testing their possible residence within the human object-recognition pathway itself. An excellent human slave candidate to test this possibility is represented by the lateral occipital cortex (LO), a mid-tier area of the ventral stream, which is a key node for shape-object perception (Malach et al., 1995). Specifically, by applying TMS stimulation over human LO (or a control site), we examined the role of LO during a VSA task, in order to directly test its role in the attentional filtering of distracting information. Crucially, we manipulated the timing of TMS application in two related experiments, in order to disentangle the contribution of LO to perceptual and attentional operations. As a result, we observed TMS modulation of activity within LO area during the attentional processing of our VSA task. By using early TMS (before stimulus display onset) and late TMS (during stimulus display onset) application over LO cortex, we obtained more general perceptual enhancement and more specific improvement of attentional filtering, respectively. We can therefore conclude that human slave LO area contains internal attentional microcircuits necessary for attentional target selection and distractor filtering.
Any natural visual environment contains a huge collection of objects, which impact on our perception and compete for drawing our interest and therefore for being preferentially noticed. By effectively selecting a relevant fraction of the incoming information for further in-depth processing, visual selective attention (VSA) optimizes vision in order to overcome the intrinsically limited computational capacity of the visual system. Single-unit recording studies have demonstrated that multiple stimuli simultaneously impinging onto the receptive field (RF) of a given neuron compete for controlling its firing by interacting with each other through mutual inhibition (Reynold & Chelazzi, 2004; Chelazzi et al., 2011; see also Biased competition model by Moran & Desimone, 1985). Thus, neural responses to stimulus pairs in the RF approximate a weighted average of the responses elicited by individual stimuli (for further details, see Reynold & Chelazzi, 2004; Chelazzi et al., 2011; see also Normalization model by Reynolds et al., 1999). The crucial question to ask is how the competition is resolved. Neurophysiological studies have shown that when two stimuli are simultaneously presented within the same receptive field (RF), neuronal responses in the absence of attentional control are largely determined by the strongest or most salient stimulus, e.g. the one presented at higher luminance contrast, which stands conspicuously against the background (Reynolds & Desimone, 2003). This reflects a bottom-up biasing of the competition on the basis of stimulus saliency. Crucially, top-down attentional control can resolve the competition between stimuli in favor of the most behaviorally relevant stimulus (target) by specifying its properties. In other words, attention can switch control of the neuronal response to the stimulus of interest, independently of its saliency, so that the target will determine the response of that neuron; in other words, the response of a given neuron to a pair of stimuli impinging on its RF will equate the neuronal response to the target stimulus, when presented alone. As a consequence, the neuronal representation of the target is enhanced within visual areas at the expense of the visual representation of the distractor (Corbetta et al., 1990; Treue & Trujillo, 1999; Luck et al., 2000, for reviews, see Chelazzi et al., 2011; Carrasco, 2011; Roe et al., 2012). Importantly, there is a wide range of observations which describe the impact of attention on sensory representations along the visual pathway. Crucially, attentional biasing of the neuronal activity within visual cortices is not uniform, but rather results in different forms of neuronal modulation (see e.g. Treue & Martinez Trujillo, 1999; Fries et al., 2001, 2008; Martinez-Trujillo & Treue, 2002; Carrasco et al., 2000; Carrasco, 2006). The traditional view of VSA maintains that attentional control is organized in a master-slave hierarchical manner: Modulatory top-down signals from a distributed frontoparietal attentional network (e.g. Moore, Armstrong, 2003; Wardak et al., 2004; Silvanto et al., 2006) - the master - impact on sensory (visual) cortical areas - the slave. In other words, lower-order sensory areas execute visual representations commanded via feedback projections from higher-order centers. Recent research has greatly challenged this conventional view, leading to the new and striking hypothesis that master centers do not have an exclusive role in attentional control, but rather the slave ventral (and dorsal) visual pathway areas might capitalize on their internal microcircuitry to directly instantiate attentional mechanisms even in the absence of control from master centers (e.g. Reynolds & Heeger, 2009; Baluch & Itti, 2011). Interestingly, a behavioral assessment following circumscribed lesions of macaque areas V4 and TEO showed a strong impairment in the animal ability to select a stimulus based on its behavioral relevance while discarding other, perceptually more conspicuous stimuli; in other word, after lesions to those areas, the behavior of the animal was at the mercy of stimulus salience (De Weerd et al., 1999; see also Gallant et al., 2000 for analogous findings in humans). These areas along the ventral pathway have therefore been claimed as essential for the instantiation of attentional mechanisms, and in particular mechanisms for the efficient filtering of non-relevant distractors (De Weerd et al., 1999; Chelazzi et al., 2011). The aim of the present study is to extend the current understanding of the brain mechanisms underlying VSA, by directly testing their possible residence within the human object-recognition pathway itself. An excellent human slave candidate to test this possibility is represented by the lateral occipital cortex (LO), a mid-tier area of the ventral stream, which is a key node for shape-object perception (Malach et al., 1995). Specifically, by applying TMS stimulation over human LO (or a control site), we examined the role of LO during a VSA task, in order to directly test its role in the attentional filtering of distracting information. Crucially, we manipulated the timing of TMS application in two related experiments, in order to disentangle the contribution of LO to perceptual and attentional operations. As a result, we observed TMS modulation of activity within LO area during the attentional processing of our VSA task. By using early TMS (before stimulus display onset) and late TMS (during stimulus display onset) application over LO cortex, we obtained more general perceptual enhancement and more specific improvement of attentional filtering, respectively. We can therefore conclude that human slave LO area contains internal attentional microcircuits necessary for attentional target selection and distractor filtering.

This review examines brain and cognitive processes involved in arithmetic. I take a distinctly developmental perspective because neither the cognitive nor the brain processes involved in arithmetic can be adequately understood outside the framework of how developmental processes unfold. I review four basic neurocognitive processes involved in arithmetic, highlighting (1) the role of core dorsal parietal and ventral temporal-occipital cortex systems that form basic building blocks from which number form and quantity representations are constructed in the brain; (2) procedural and working memory systems anchored in the basal ganglia and frontoparietal circuits, which create short-term representations that allow manipulation of multiple discrete quantities over several seconds; (3) episodic and semantic memory systems anchored in the medial and lateral temporal cortex that play an important role in long-term memory formation and generalization beyond individual problem attributes; and (4) prefrontal cortex control processes that guide allocation of attention resources and retrieval of facts from memory in the service of goal-directed problem solving. Next I examine arithmetic in the developing brain, first focusing on studies comparing arithmetic in children and adults, and then on studies examining development in children during critical stages of skill acquisition. I highlight neurodevelopmental models that go beyond parietal cortex regions involved in number processing, and demonstrate that brain systems and circuits in the developing child brain are clearly not the same as those seen in more mature adult brains sculpted by years of learning. The implications of these findings for a more comprehensive view of the neural basis of arithmetic in both children and adults are discussed.

The supratentorial level consists of 2 main anatomical regions: the diencephalon and the telencephalon. The anatomy, physiology, and clinical correlations of lesions affecting the diencephalon and visual pathways are described in another chapter. The telencephalon forms the cerebral hemispheres, which consist of the cerebral cortex, basal ganglia, and subcortical white matter tracts that interconnect areas of the cerebral cortex with one another and with the basal ganglia, thalamus, brainstem, and spinal cord. The medial portion of the cerebral hemispheres includes the amygdala, hippocampal formation, and cingulate cortex. These areas are involved in emotional and memory processing. The olfactory system is intimately related to these structures. The lateral and inferior aspects of the cerebral hemispheres include most of the frontal, insular, parietal, temporal, and occipital lobes. Neurons distributed in several cortical areas interact, forming functional networks that control different cognitive functions.

In the paper discussed in this chapter, the authors were interested in the neural underpinnings for facial beauty and whether such responses were automatic. In a functional magnetic resonance imaging study over two sessions, the authors asked participants to make beauty and identity judgments on a series of computer-generated faces. When people judged beauty, the authors found that neural activity varied parametrically to the degree of facial attractiveness in the fusiform face area and the lateral occipital complex, as well as in parts of parietal and frontal cortices. When people made familiarity judgments, the authors observed the same modulation of neural activity within occipital cortex to the degree of attractiveness in the faces. The data suggested that human brains automatically respond to facial beauty even when people might be attending to other aspects of the faces they apprehend.

This chapter discusses the anatomic basis related to control of head and trunk posture, and symptom and syndromes caused by its impairment. The spinal cord contains machinery for stepping, the locomotor generator. However, the spinal cord is under the control of supraspinal centers. In human walking, intention or attention takes part to various degrees, from fully attended walking to nearly automatic walking. Multiple structures of the central nervous system are known to be involved in the central control of walking. In addition to the sensorimotor areas directly related to leg movement such as the pre-SMA, SMA proper, anterior cingulate gyrus, lateral premotor areas, and the foot areas of the primary sensorimotor cortices, the cortical areas related to visual information processing, such as the occipital cortex and the posterior parietal area, are also important. Furthermore, the brainstem gait center, cerebellum, and basal ganglia also play an important part.

Human observers can reliably segment visual input and recognise objects. However, the underlying processes happen so quickly that they normally cannot be captured with fMRI. We used Emerging Images (EI), which contains a hidden object and extends the process of recognition, to investigate the involvement of early visual areas (V1, V2 and V3) and lateral occipital complex (LOC) in object recognition. The early visual areas were located with a retinotopy scan and the LOC with a localiser. The participants (N=8) then viewed an EI, followed by the hidden object’s silhouette (disambiguation), and then, the EI was repeated. BOLD responses before and after disambiguation were compared. The retinotopy parameters were used to back-project the BOLD response onto the visual field, creating spatially detailed maps of the activity change. V1 and V2 (but not V3) showed stronger response after disambiguation, while there was no difference in the LOC. The back-projections revealed no distinct pattern or changes in activity on object location, indicating that the activity in V1 and V2 is not specific for voxels corresponding to the object location. We found no difference before and after disambiguation in the LOC, which may be repetition suppression counteracting the effect of recognition.

Inside our heads is a magnificent structure that controls our actions and somehow evokes an awareness of the world around. Yet, as Alan Turing once put it, it resembles nothing so much as a bowl of cold porridge! It is hard to see how an object of such unpromising appearance can achieve the miracles that we know it to be capable of. Closer examination, however, begins to reveal the brain as having a much more intricate structure and sophisticated organization. The large convoluted (and most porridge-like) portion on top is referred to as the cerebrum. It is divided cleanly down the middle into left and right cerebral hemispheres, and considerably less cleanly front and back into the frontal lobe and three other lobes: the parietal, temporal and occipital. Further down, and at the back lies a rather smaller, somewhat spherical portion of the brain - perhaps resembling two balls of wool - the cerebellum. Deep inside, and somewhat hidden under the cerebrum, lie a number of curious and complicated-looking different structures: the pons and medulla (including the reticular formation, a region that will concern us later) which constitute the brain-stem, the thalamus, hypothalamus, hippocampus, corpus callosum, and many other strange and oddly named constructions. The part that human beings feel that they should be proudest of is the cerebrum - for that is not only the largest part of the human brain, but it is also larger, in its proportion of the brain as a whole, in man than in other animals. (The cerebellum is also larger in man than in most other animals.) The cerebrum and cerebellum have comparatively thin outer surface layers of grey matter and larger inner regions of white matter. These regions of grey matter are referred to as, respectively, the cerebral cortex and the cerebellar cortex. The grey matter is where various kinds of computational task appear to be performed, while the white matter consists of long nerve fibres carrying signals from one part of the brain to another. Various parts of the cerebral cortex are associated with very specific functions.

Context: Lacunar infarcts are small infarcts caused by occlusion of a single penetrating vessel, affecting mostly the basal ganglia, subcortical white matter and pons1. Around 20-30% of patients may progress symptoms over hours to days, and this presentation is associated with disability and poor prognosis2. Case report: A 70-year-old man with history of smoking, hypertension and a previous right occipital stroke reported right upper lip paresthesias since awakening. In 2-hours the right perioral region and his right hand were affected. After 3-hours he noted slurred speech. After 4-hours, imbalance was added to the previous symptoms. On admission, NIHSS was 4, mostly by previous left hemianopia, new right arm ataxia and cerebellar dysarthria. There were no weakness or sensory déficits. Brain MRI showed a subacute lacunar stroke in the left thalamus. Discussion: Thalamic lacunar strokes can present in a wide range of symptoms depending on the affected nuclei. The ventral posterior lateral nucleus (VPLn) and the ventral posterior medial nucleus (VPMn) carries sensory input from the contralateral body and face, respectively3. Cheiro-oral syndrome (COS) is considered a pure sensory thalamic lacunar syndrome with symptoms that affect the face, hand and/or foot, but may be accompanied by ipsilateral ataxia if the ventral lateral nucleus is also affected4 . Although classically associated with thalamic ischemic lesions, there are descriptions of hemorrhagic strokes5 and multiple different affected regions presenting as COS, including brainstem5 , internal capsule6 , operculum7 , cortex8 , corona radiata9 and thalamus10. Early recognition and diagnosis is essencial to institute adequate early treatment and secondary prophylaxis.