The contribution of LM to the neuroscience of movement vision

Akinetopsia (visual motion blindness) associated with brain metastases: a case report

Akinetopsia is a rare neurological syndrome characterized by an impaired perception of movement, often resulting from brain damage due to ischemia, epilepsy, or medication. It is also known as visual motion blindness, and patients with this condition are unable to perceive motion normally even with perfect visual acuity. This report aims to present a case of a patient in their late 40 s who developed akinetopsia and also an impairment in movement perception of objects without emitting sounds, after experiencing a late relapse of breast cancer with the occurrence of multiple brain metastases. The patient also experienced visual hallucinations, night terrors, and difficulty forming anterograde memory. Neuroimaging with MRI revealed severe brain damage, especially in the middle temporal area of the visual cortex. Akinetopsia is a rare phenomenon, and this is the first known case of its association with brain metastases.

How are patterned movements stored in working memory?

Introduction

In this study, the change detection paradigm was used to study the working memory of patterned movements and the relationship of this type of memory with the visuospatial sketchpad in three experiments.

Methods

Experiment 1 measured participants' working memory capacity for patterned movements and explored the influence of stimulus type with indicators such as response time and accuracy rate. Experiments 2 and 3 explored the relationship between patterned movements and the visual and spatial subsystems, respectively.

Results

The results of Experiment 1 indicated that individuals can store 3-4 patterned movements in working memory; however, a change in stimulus format or an increase in memory load may decrease the speed and efficiency of working memory processing. The results of Experiment 2 showed that working memory and visual working memory are independent when processing patterned movements. The results of Experiment 3 showed that the working memory of patterned movements was affected by spatial working memory.

Discussion

Changes in stimulus type and memory load exerted different effects on the working memory capacity of participants. These results provide behavioral evidence that the storage of patterned movement information is independent of the visual subsystem but requires the spatial subsystem of the visuospatial sketchpad.

Visual Cortical Area MT Is Required for Development of the Dorsal Stream and Associated Visuomotor Behaviors

The middle temporal (MT) area of the extrastriate visual cortex has long been studied in adulthood for its distinctive physiological properties and function as a part of the dorsal stream, yet interestingly it possesses a similar maturation profile as the primary visual cortex (V1). Here, we examined whether an early-life lesion in MT of marmoset monkeys (six female, two male) altered the dorsal stream development and the behavioral precision of reaching-to-grasp sequences. We observed permanent changes in the anatomy of cortices associated with both reaching (parietal and medial intraparietal areas) and grasping (anterior intraparietal area), as well as in reaching-and-grasping behaviors. In addition, we observed a significant impact on the anatomy of V1 and the direction sensitivity of V1 neurons in the lesion projection zone. These findings indicate that area MT is a crucial node in the development of primate vision, affecting both V1 and areas in the dorsal visual pathway known to mediate visually guided manual behaviors.SIGNIFICANCE STATEMENT Previous studies have identified a role for the MT area of the visual cortex in perceiving motion, yet none have examined its central role in the development of the visual cortex and in the establishment of visuomotor behaviors. To address this, we used a unilateral MT lesion model in neonatal marmosets before examining the anatomic, physiological, and behavioral consequences. In adulthood, we observed perturbations in goal-orientated reach-and-grasp behavior, altered direction selectivity of V1 neurons, and changes in the cytoarchitecture throughout dorsal stream areas. This study highlights the importance of MT as a central node in visual system development and consequential visuomotor activity.

Children with cerebral palsy display altered neural oscillations within the visual MT/V5 cortices

Cortical visual processing in visual MT/V5 is necessary for tracking movement and performing reliable visuomotor transformations. Although the role of this cortical area is well recognized, the activity of the visual MT/V5 cortical area in children with cerebral palsy (CP) has not been examined nor has its potential role in the atypical motor actions of these children been considered. This study used magnetoencephalography to image the neural activity in the motion-sensitive MT/V5 cortices of typically developing (TD) children (n = 21; mean age 14 yrs. ± 2, 12 males) and children with CP (n = 21; mean age 16 yrs. ± 4, 13 males) as they viewed a horizontally moving stimulus. Behavioral measures of visual perception were additionally assessed by having the participants press a button when the visual stimulus changed to moving in vertical direction. Our results showed that the horizontal movement of the visual stimulus evoked changes in the strength of the theta-alpha (5-10 Hz) and alpha-beta (8-20 Hz) oscillations in the visual MT/V5 area of all participants. Compared with the TD children, the children with CP had weaker alpha-beta oscillations in the visual MT/V5 cortices. In addition, the children with CP took longer to perceive a directional change of the visual stimulus and made more errors in detecting the change. Lastly, weaker alpha-beta oscillations were correlated with slower detection of the change in motion direction and less accuracy in identifying the change. This study shows that the uncharacteristic neural oscillations in the visual MT/V5 cortical area may partially account for the abnormal perceptions and motor decisions seen in children with CP.

A probabilistic atlas of the human motion complex built from large-scale functional localizer data

Accurate motion perception is critical to dealing with the changing dynamics of our visual world. A cluster known as the human MT+ complex (hMT+) has been identified as a core region involved in motion perception. Several atlases defined based on cytoarchitecture, retinotopy, connectivity, and multimodal features include homologs of the hMT+. However, an hMT+ atlas defined directly based on this region's response for motion is still lacking. Here, we identified the hMT+ based on motion responses from functional magnetic resonance imaging (fMRI) localizer data in 509 participants and then built a probabilistic atlas of the hMT+. As a result, four main findings were revealed. First, the hMT+ showed large interindividual variability across participants. Second, the atlases stabilized when the number of participants used to build the atlas was more than 100. Third, the functional hMT+ showed good agreement with the hMT+ atlases built based on cytoarchitecture, retinotopy, and connectivity, suggesting a good structural-functional correspondence. Fourth, tests on multiple fMRI data sets acquired from independent participants, imaging parameters and paradigms revealed that the functional hMT+ showed higher sensitivity than all other atlases in ROI analysis except that connectivity and multimodal hMT+ atlases in the left hemisphere could infrequently attain comparable sensitivity to the functional atlas. Taken together, our findings reveal the benefit of using large-scale functional localizer data to build a reliable and representative hMT+ atlas. Our atlas is freely available for download; it can be used to localize the hMT+ in individual participants when functional localizer data are not available.

The effect of target speed on perception of visual motion direction in a patient with akinetopsia

Although much research has been devoted to the neural correlates of motion perception, the processing of speed of motion is still a topic of discussion. Apart from patient LM, no in-depth clinical research has been done in the past 20 years on this topic. In the present study, we investigated patient TD, who suffered from the rare disorder akinetopsia due to bilateral lesions of V5 after stroke. By means of a Random-Dot-Kinematogram (RDK) in which speed was varied systematically, it was found that TD was impaired in perceiving the direction of movement at speeds exceeding 9 deg/s. Our study suggests that V5 plays an important role in processing high-speed visual motion and further implies that V5 does not play a crucial role in processing low-speed visual motion. A remarkable finding, which has not been shown before, was that TD always reported the opposite direction of the actual movement at a speed of 24 deg/s. This suggests a form of the continuous wagon wheel illusion, which might have been caused by intact brain areas operating at different sampling rates than area V5.

The value of cognitive neuropsychology: The case of vision research

Cognitive neuropsychological evidence is widely viewed as inherently flawed or weak, despite well-reasoned arguments to the contrary by many theorists. Rather than attempting yet another defence of cognitive neuropsychology on logical grounds, we point out through examples that in practice, cognitive neuropsychological evidence is widely accepted as valid and important, and has had a major impact on cognitive theory and research. Objections offered in the abstract rarely arise in the context of actual studies. We develop these points through examples from the domain of vision, discussing cerebral achromatopsia and akinetopsia, selective impairment and sparing of face recognition, perception-action dissociations, and blindsight.

The contribution of single case studies to the neuroscience of vision

Visual neuroscience is concerned with the neurobiological foundations of visual perception, that is, the morphological, physiological, and functional organization of the visual brain and its co-operative partners. One important approach for understanding the functional organization of the visual brain is the study of visual perception from the pathological perspective. The study of patients with focal injury to the visual brain allows conclusions about the representation of visual perceptual functions in the framework of association and dissociation of functions. Selective disorders have been reported for more "elementary" visual capabilities, for example, color and movement vision, but also for visuo-cognitive capacities, such as visual agnosia or the visual field of attention. Because these visual disorders occur rather seldom as selective and specific dysfunctions, single cases have always played, and still play, a significant role in gaining insights into the functional organization of the visual brain.

Two Visual Pathways in Primates Based on Sampling of Space: Exploitation and Exploration of Visual Information

Evidence is strong that the visual pathway is segregated into two distinct streams—ventral and dorsal. Two proposals theorize that the pathways are segregated in function: The ventral stream processes information about object identity, whereas the dorsal stream, according to one model, processes information about either object location, and according to another, is responsible in executing movements under visual control. The models are influential; however recent experimental evidence challenges them, e.g., the ventral stream is not solely responsible for object recognition; conversely, its function is not strictly limited to object vision; the dorsal stream is not responsible by itself for spatial vision or visuomotor control; conversely, its function extends beyond vision or visuomotor control. In their place, we suggest a robust dichotomy consisting of a ventral stream selectively sampling high-resolution/focal spaces, and a dorsal stream sampling nearly all of space with reduced foveal bias. The proposal hews closely to the theme of embodied cognition: Function arises as a consequence of an extant sensory underpinning. A continuous, not sharp, segregation based on function emerges, and carries with it an undercurrent of an exploitation-exploration dichotomy. Under this interpretation, cells of the ventral stream, which individually have more punctate receptive fields that generally include the fovea or parafovea, provide detailed information about object shapes and features and lead to the systematic exploitation of said information; cells of the dorsal stream, which individually have large receptive fields, contribute to visuospatial perception, provide information about the presence/absence of salient objects and their locations for novel exploration and subsequent exploitation by the ventral stream or, under certain conditions, the dorsal stream. We leverage the dichotomy to unify neuropsychological cases under a common umbrella, account for the increased prevalence of multisensory integration in the dorsal stream under a Bayesian framework, predict conditions under which object recognition utilizes the ventral or dorsal stream, and explain why cells of the dorsal stream drive sensorimotor control and motion processing and have poorer feature selectivity. Finally, the model speculates on a dynamic interaction between the two streams that underscores a unified, seamless perception. Existing theories are subsumed under our proposal.

Activation of the Human MT Complex by Motion in Depth Induced by a Moving Cast Shadow

A moving cast shadow is a powerful monocular depth cue for motion perception in depth. For example, when a cast shadow moves away from or toward an object in a two-dimensional plane, the object appears to move toward or away from the observer in depth, respectively, whereas the size and position of the object are constant. Although the cortical mechanisms underlying motion perception in depth by cast shadow are unknown, the human MT complex (hMT+) is likely involved in the process, as it is sensitive to motion in depth represented by binocular depth cues. In the present study, we examined this possibility by using a functional magnetic resonance imaging (fMRI) technique. First, we identified the cortical regions sensitive to the motion of a square in depth represented via binocular disparity. Consistent with previous studies, we observed significant activation in the bilateral hMT+, and defined functional regions of interest (ROIs) there. We then investigated the activity of the ROIs during observation of the following stimuli: 1) a central square that appeared to move back and forth via a moving cast shadow (mCS); 2) a segmented and scrambled cast shadow presented beside the square (sCS); and 3) no cast shadow (nCS). Participants perceived motion of the square in depth in the mCS condition only. The activity of the hMT+ was significantly higher in the mCS compared with the sCS and nCS conditions. Moreover, the hMT+ was activated equally in both hemispheres in the mCS condition, despite presentation of the cast shadow in the bottom-right quadrant of the stimulus. Perception of the square moving in depth across visual hemifields may be reflected in the bilateral activation of the hMT+. We concluded that the hMT+ is involved in motion perception in depth induced by moving cast shadow and by binocular disparity.

Some Unusual Neuropsychological Syndromes: Somatoparaphrenia, Akinetopsia, Reduplicative Paramnesia, Autotopagnosia

Some unusual neuropsychological syndromes are rarely reported in the neuropsychological literature. This paper presents a review of four of these unusual clinical syndromes: (1) somatoparaphrenia (delusional belief in which a patient states that the limb contralateral to a brain pathology, does not belong to him/her); (2) akinetopsia (cortical syndrome in which patient losses the ability to perceive visual motion); (3) reduplicative paramnesia (believe that a familiar place, person, object, or body part has been duplicated); and (4) autotopagnosia (disturbance of body schema involving the loss of ability to localize, recognize, or identify the specific parts of one's body). It is concluded that regardless of their rarity, it is fundamental to take them into consideration in order to understand how the brain organizes cognition; their understanding is also crucial in the clinical analysis of patients with brain pathologies.