Light sensitivity in cortical scotomata contralateral to small islands of blindness

Summary Detailed perimetry was performed on two patients with extensive defects in one half of the visual field together with the presence of small scotomata in the opposite visual field. In both cases, visual function can be demonstrated within the major scotoma, but only in a small region that occupies a mirror-symmetric position with the small scotoma in the opposite half of the field. These results are analogous to an earlier finding by Sprague in the cat, and suggest that interhemispheric interactions in man are organized with a symmetric topography.     

Transition from monocular motion perception to dichoptic motion perception as a function of the stimulus duration

We have recently developed a new motion display in which the monocular and dichoptic motion components move in opposite directions (Hayashi et al. 2007). In the present paper, we estimated the difference between the integration times required to detect the dichoptic motion and monocular motion by changing the duration of the stimulus. The results showed that monocular motion perception becomes more dominant as the stimulus duration becomes shorter, indicating that the detection of dichoptic motion is relatively slow process that requires a longer integration time compared with the process used to detect monocular motion.     

Permanent bilateral cortical blindness due to reversible posterior leukoencephalopathy syndrome

Reversible posterior leukoencephalopathy syndrome (RPLS) is induced by acute cerebral edema. Its symptoms include seizures, headache, altered mental status, and visual disturbances. The clinical and radiological findings are usually transient. This report describes a case of RPLS resulting in bilateral total blindness. A 40-year-old man presented with lethargy and bilateral visual loss. He had a 20-year history of hypertension, but had never been treated. On presentation, the left eye was able to perceive light, but the right eye was not. Radiological examination showed diffuse edema in the brain, and ocular fundus examination revealed severe bilateral hypertensive retinopathy. Antihypertensive therapy improved the patient's general condition, including blood pressure. Radiological findings 5 months later showed resolution of most of the abnormal signal areas. However, total blindness had developed in both eyes by day 15, and two courses of pulsed corticosteroid therapy failed to restore the visual loss.     

Functional magnetic resonance imaging mirrors recovery of visual perception after repetitive tachistoscopic stimulation in patients with partial cortical blindness

We investigated three patients with partial cortical blindness after brain injury by means of functional magnetic resonance imaging (fMRI) before and after the application of a daily visual stimulation-therapy over a period of 6 months. Before therapy, fMRI data showed a severely reduced blood-oxygen-level-dependent (BOLD) signal in primary visual cortex when compared to healthy volunteers. Following several months of rehabilitative therapy a neuropsychological improvement of visual functions was accompanied by an increase in BOLD signal of residual perilesional regions whereas fMRI data of the control group remained unchanged. A high capacity of functional recovery and synaptic plasticity of surviving perilesional neuronal structures of primary visual cortex followed by an increased input into post-connected visual areas can be discussed as a basis for the reoccurrence of visual functions.     

Movement-related gating of climbing fibre input to cerebellar cortical zones

The inferior olive climbing fibre projection and associated spino-olivocerebellar paths (SOCPs) have been studied intensively over the last quarter of a century yet precisely what information they signal to the cerebellar cortex during movements remains unclear. A different approach is to consider the times during a movement when afferent signals are likely to be conveyed via these paths. Central regulation (gating) of afferent transmission during active movements is well documented in sensory pathways leading to the cerebral cortex and the present review examines the possibility that a similar phenomenon also occurs in SOCPs during movements such as locomotion and reaching. Several lines of evidence are considered which suggest that SOCPs are not always open for transmission. Instead, flow of sensory information to the cerebellum via climbing fibre paths is powerfully modulated during active movements. The findings are discussed in relation to the parasagittal zonal organization of the cerebellar cortex and, in particular, evidence is presented that different cerebellar zones are subject to similar patterns of gating during reaching but can differ appreciably in the pattern of modulation their SOCPs exhibit during locomotion. Furthermore, differences in gating can occur at different rostrocaudal loci within the same zone, suggesting that in the awake behaving animal, individual cerebellar zones are not functionally homogeneous. Finally, the data are interpreted in relation to the error detector hypothesis of climbing fibre function and the possibility explored that the gating serves as a task-dependent mechanism that operates to prevent self-generated 'irrelevant' sensory inputs from being relayed via the SOCPs to the cerebellar cortex, while behaviourally 'relevant' signals are selected for transmission.     

Influence of visual motion on tactile motion perception

Subjects were presented with pairs of tactile drifting sinusoids and made speed discrimination judgments. On some trials, a visual drifting sinusoid, which subjects were instructed to ignore, was presented simultaneously with one of the two tactile stimuli. When the visual and tactile gratings drifted in the same direction (i.e., from left to right), the visual distractors were found to increase the perceived speed of the tactile gratings. The effect of the visual distractors was proportional to their temporal frequency but not to their perceived speed. When the visual and tactile gratings drifted in opposite directions, the distracting effect of the visual distractors was either substantially reduced or, in some cases, reversed (i.e., the distractors slowed the perceived speed of the tactile gratings). This result suggests that the observed visual-tactile interaction is dependent on motion and not simply on the oscillations inherent in drifting sinusoids. Finally, we find that disrupting the temporal synchrony between the visual and tactile stimuli eliminates the distracting effect of the visual stimulus. We interpret this latter finding as evidence that the observed visual-tactile interaction operates at the sensory level and does not simply reflect a response bias.     

Frequency of color blindness among Nigerian school children in Lagos

Plates 1–15 of the Ishihara tests for color blindness were administered to 5,580 boys and 5,405 girls in primary and secondary schools in Lagos. The difference between males and females in the frequency of total color blindness was not significant. The frequency of total color blindness among the children was 0.19%. However, the frequencies of red-green color blindness, which were 3.60% and 0.81% among the males and females, respectively, were significantly different. Deutans occurred at a higher frequency than protans among both male and female red-green color blind individuals, but the differences among males and also females were not significant. In addition, there was no significant difference between the sexes in the occurrence of deutans and protans. Although the frequency of red-green color blindness detected among males in this study is significantly lower than that reported for Lagos in another survey, which gave a frequency similar to that for Caucasians, the frequency obtained in the present study is similar to frequencies reported for other populations of Blacks of African Ancestry. Am. J. Hum. Biol. 10:283–288, 1998. © 1998 Wiley-Liss, Inc.     

Natural facial motion enhances cortical responses to faces

The ability to perceive facial motion is important to successfully interact in social environments. Previously, imaging studies have investigated neural correlates of facial motion primarily using abstract motion stimuli. Here, we studied how the brain processes natural non-rigid facial motion in direct comparison to static stimuli and matched phase-scrambled controls. As predicted from previous studies, dynamic faces elicit higher responses than static faces in lateral temporal areas corresponding to hMT+/V5 and STS. Interestingly, individually defined, static-face-sensitive regions in bilateral fusiform gyrus and left inferior occipital gyrus also respond more to dynamic than static faces. These results suggest integration of form and motion information during the processing of dynamic faces even in ventral temporal and inferior lateral occipital areas. In addition, our results show that dynamic stimuli are a robust tool to localize areas related to the processing of static and dynamic face information. J. Schultz and K. S. Pilz have contributed equally to this work.     

Suprathreshold asymmetries in human motion perception

Detection of asymmetries has been a mainstay of using vestibular reflexes to assess semicircular canal function. However, there has been relatively little work on how vestibular stimuli are perceived. Suprathreshold vestibular perception was measured in 13 normal healthy controls by having them compare the relative sizes of two yaw (vertical-axis rotation) or sway (right–left translation) stimuli. Both stimuli were 1.5 s in duration with a staircase used to adjust the relative size of the stimuli to find a pair of stimuli perceived as equal. Motion stimuli were delivered in darkness using a hexapod motion platform, and visual stimuli simulating motion were presented on a screen in the absence of platform motion. Both same direction (SD) and opposite direction (OD) stimuli were delivered in separate runs. After a two-interval stimulus, subjects reported which movement they perceived as larger. Cumulative distribution functions were fit to the responses so that the relative magnitudes of the two stimuli perceived as equal could be determined. For OD trial blocks, a directional asymmetry index was calculated to compare the relative size of perceived rightward and leftward motion. For all trial blocks, a temporal asymmetry index (TAI) was used to compare the relative size of the first and second intervals. Motion OD stimuli were perceived as equal in all subjects in yaw and all but one in sway. For visual OD stimuli, two subjects had slightly asymmetric responses for both sway and yaw. The TAI demonstrated asymmetry in 54 % in yaw, in which the second interval was perceived to be larger in all but one subject who had an asymmetry. For sway, only two subjects had a significant asymmetry. Visual stimuli produced a similar rate of asymmetry. The direction and magnitude of these asymmetries were not significantly correlated with those seen for motion stimuli. Asymmetries were found in a fraction with the TAI in SD stimuli for motion in yaw (42 %) and sway (33 %), as well as for vision in yaw (60 %) and sway (43 %). The precision at discriminating SD motion stimuli decreased significantly with age, but there was no difference in OD motion or visual stimuli.     

Auditory motion affects visual motion perception in a speeded discrimination task

Transient auditory stimuli have been shown to influence the perception of ambiguous 2D visual motion displays (the bouncing-disks effect; e.g. Sekuler et al. in Nature 385:308, 1997). The question addressed here was whether continuous moving auditory stimuli can also influence visual motion perception under the same experimental conditions. In Experiment 1, we used a modification of Sanabria et al.'s (Exp Brain Res 157:537-541, 2004) paradigm (involving an indirect behavioural measure of the bouncing-disks effect), in which the 2D visual display was presented together with either a brief tone, a continuous moving sound, or in the absence of any form of auditory stimulation. Crucially, the results showed that, together with the effect of the brief tone on bouncing trials, the presence of the continuous moving sound speeded-up participants' responses on streaming trials as compared to the brief tone or no sound conditions. The results of a second experiment revealed that the effect of the continuous moving sound reported in Experiment 1 was not caused simply by the presence of continuous auditory stimulation per se.     

Using visual direction in three-dimensional motion perception

The eyes receive slightly different views of the world, and the differences between their images (binocular disparity) are used to see depth. Several authors have suggested how the brain could exploit this information for three-dimensional (3D) motion perception, but here we consider a simpler strategy. Visual direction is the angle between the direction of an object and the direction that an observer faces. Here we describe human behavioral experiments in which observers use visual direction, rather than binocular information, to estimate an object's 3D motion even though this causes them to make systematic errors. This suggests that recent models of binocular 3D motion perception may not reflect the strategies that human observers actually use.     

Laminar sources of synaptic input to cortical inhibitory interneurons and pyramidal neurons

The functional role of an individual neuron within a cortical circuit is largely determined by that neuron's synaptic input. We examined the laminar sources of local input to subtypes of cortical neurons in layer 2/3 of rat visual cortex using laser scanning photostimulation. We identified three distinct laminar patterns of excitatory input that correspond to physiological and morphological subtypes of neurons. Fast-spiking inhibitory basket cells and excitatory pyramidal neurons received strong excitatory input from middle cortical layers. In contrast, adapting inhibitory interneurons received their strongest excitatory input either from deep layers or laterally from within layer 2/3. Thus, differential laminar sources of excitatory inputs contribute to the functional diversity of cortical inhibitory interneurons.     

Topographical and laminar distribution of cortical input to the monkey entorhinal cortex

Hippocampal formation plays a prominent role in episodic memory formation and consolidation. It is likely that episodic memory representations are constructed from cortical information that is mostly funnelled through the entorhinal cortex to the hippocampus. The entorhinal cortex returns processed information to the neocortex. Retrograde tracing studies have shown that neocortical afferents to the entorhinal cortex originate almost exclusively in polymodal association cortical areas. However, the use of retrograde studies does not address the question of the laminar and topographical distribution of cortical projections within the entorhinal cortex. We examined material from 60 Macaca fascicularis monkeys in which cortical deposits of either (3)H-amino acids or biotinylated dextran-amine as anterograde tracers were made into different cortical areas (the frontal, cingulate, temporal and parietal cortices). The various cortical inputs to the entorhinal cortex present a heterogeneous topographical distribution. Some projections terminate throughout the entorhinal cortex (afferents from medial area 13 and posterior parahippocampal cortex), while others have more limited termination, with emphasis either rostrally (lateral orbitofrontal cortex, agranular insular cortex, anterior cingulate cortex, perirhinal cortex, unimodal visual association cortex), intermediate (upper bank of the superior temporal sulcus, unimodal auditory association cortex) or caudally (parietal and retrosplenial cortices). Many of these inputs overlap, particularly within the rostrolateral portion of the entorhinal cortex. Some projections were directed mainly to superficial layers (I-III) while others were heavier to deep layers (V-VI) although areas of dense projections typically spanned all layers. A primary report will provide a detailed analysis of the regional and laminar organization of these projections. Here we provide a general overview of these projections in relation to the known neuroanatomy of the entorhinal cortex.     

Theory of mind and motion perception in schizophrenia

This study investigated the relationship between theory of mind (ToM) deficits and visual perception in patients with schizophrenia (N=52; 17 remitted and unmedicated) compared with healthy controls (N=30). ToM was assessed with the Eyes Test, which asked participants to choose which of 4 words best described the mental state of a person whose eyes were depicted in a photograph. Visual perception was evaluated with form and motion coherence threshold measurements. Results revealed that patients with schizophrenia (both remitted and nonremitted) showed deficits on the Eyes Test and the motion coherence task. ToM dysfunctions were associated with higher motion coherence thresholds and more severe negative symptoms. This suggests that ToM deficits are related to motion perception dysfunctions, which indicates a possible role of motion-sensitive areas in the pathophysiology of schizophrenia.     

A cinematographic hypothesis of cortical dynamics in perception.

The aim of this study was to measure and classify spatial patterns in sensory cortical EEGs relating to conditioned stimuli (CSs) in order to test the hypothesis, based on clinical reports, that cortical dynamics is not continuous but operates in steps that resemble frames in a cinema. Recent advances in the application of the Hilbert Transform to intracranial recordings of the EEG in animals have revealed markers for repetitive phase transitions in neocortex at frame rates in the theta band. The frames were sought in multichannel EEGs that had been recorded from 8x8 high-density arrays that were fixed on primary sensory cortices of rabbits trained to discriminate visual, auditory or somatic conditioned stimuli with reinforcement (CS+) or without (CS-). Localization of frames in EEGs was by use of a new index, H(e)(t), called "pragmatic information". Each spatial pattern was represented by a feature vector from the 64 analytic amplitudes at a maximal value of H(e)(t) from the Hilbert transform and expressed as a 64x1 feature vector specifying a point in 64-space. Classification with respect to CS+/- was by calculation of Euclidean distances of points from centers of gravity of clusters after preprocessing by nonlinear mapping. Stable spatial patterns were found in the form of amplitude modulation (AM) of aperiodic waveforms that included all channels. The impact of a CS on a sensory neocortex reorganized background EEG into two types of sequential patterns of coordinated activity, initially local and modality-specific, later global. The initial stage of phase transitions required 3-7 ms. Large-scale cortical activity then reorganized itself repeatedly and reliably over relatively immense cortical distances within the cycle duration of the center frequency of oscillation. The size, texture, timing, and duration of the AM patterns support the hypothesis that these frames may provide the basis for multisensory percepts (Gestalts).     

Evidence for spatial structure in the cortical input to the monkey lateral geniculate nucleus

Summary We combined visual stimulation of the corticogeniculate pathway with cryogenic blockade of area 17 to examine the visual spatial structure of the cortical influence on single macaque LGN cells. Excitatory central areas surrounded by inhibitory regions and vice versa were found with equal frequency. Unstructured influences were also seen. The structure of the influence suggests that modulation of the spatial parameter may be an important function for the corticogeniculate pathway.