Deficits and recovery of first‐ and second‐order motion perception in patients with unilateral cortical lesions

Unilateral lesions in the posterior parietal cortex can degrade motion perception in the contralesional visual hemifield. Our aim was to investigate whether deficits caused by cortical lesions may be different for first- and second-order motion perception, and to study the time scale of any potential recovery. In nine patients with circumscribed lesions mainly in the parietal and fronto-parietal cortex, thresholds for direction discrimination were measured for stimuli presented peripherally in their ipsi- and contralesional hemifield. Subjects had to identify the direction of a vertically moving object embedded in a background of dynamic random dot noise. The object consisted of various proportions of signal and noise dots. Signal dots were either (a) coherently moving in the same direction as the object (first-order), (b) stationary (second-order: drift-balanced), or (c) coherently moving in the opposite direction (second-order: theta). Noise dots were flickering. Two patients showed significant threshold elevations for all three types of motion stimuli presented in their contralesional hemifield, while thresholds for ipsilesional targets were unaffected. Neither showed any selective deficit of first- versus second-order motion perception, but second-order motion was more impaired. Their lesions probably included the motion area V5-MT, which was spared in the other seven patients. One of the patients, who was retested several times during a 27-month postlesional period, showed complete recovery for first- and second-order motion direction discrimination, as well as for the detection of speed differences.     

Direction-specific motion blindness induced by focal stimulation of human extrastriate cortex

Motion blindness (MB) or akinetopsia is the selective disturbance of visual motion perception while other features of the visual scene such as colour and shape are normally perceived. Chronic and transient forms of MB are characterized by a global deficit of direction discrimination (pandirectional), which is generally assumed to result from damage to, or interference with, the motion complex MT+/V5. However, the most characteristic feature of primate MT-neurons is not their motion specificity, but their preference for one direction of motion (direction specificity). Here, we report that focal electrical stimulation in the human posterior temporal lobe selectively impaired the perception of motion in one direction while the perception of motion in other directions was completely normal (unidirectional MB). In addition, the direction of MB was found to depend on the brain area stimulated. It is argued that direction specificity for visual motion is not only represented at the single neuron level, but also in much larger cortical units.     

Gangliosides fail to enhance behavioral recovery after bilateral ablation of the visual cortex

Postsurgical injections of GM1 gangliosides (30 mg/kg IP) reduced neither behavioral deficits in rats following bilateral ablation of the visual cortex nor the extent of retrograde degeneration of neurons in the dorsolateral geniculate nucleus that typically accompanies large lesions of the visual cortex. Our findings are in contrast to previous research, in which ganglioside treatments have been shown to enhance the rate of functional recovery after lesions in other parts of the central nervous system. The negative findings in the present experiment may be due to the disruption of normal circadian rhythms caused by occipital cortex injury.     

Binding of motion and colour is early and automatic

At what stages of the human visual hierarchy different features are bound together, and whether this binding requires attention, is still highly debated. We used a colour-contingent motion after-effect (CCMAE) to study the binding of colour and motion signals. The logic of our approach was as follows: if CCMAEs can be evoked by targeted adaptation of early motion processing stages, without allowing for feedback from higher motion integration stages, then this would support our hypothesis that colour and motion are bound automatically on the basis of spatiotemporally local information. Our results show for the first time that CCMAE's can be evoked by adaptation to a locally paired opposite-motion dot display, a stimulus that, importantly, is known to trigger direction-specific responses in the primary visual cortex yet results in strong inhibition of the directional responses in area MT of macaques as well as in area MT+ in humans and, indeed, is perceived only as motionless flicker. The magnitude of the CCMAE in the locally paired condition was not significantly different from control conditions where the different directions were spatiotemporally separated (i.e. not locally paired) and therefore perceived as two moving fields. These findings provide evidence that adaptation at an early, local motion stage, and only adaptation at this stage, underlies this CCMAE, which in turn implies that spatiotemporally coincident colour and motion signals are bound automatically, most probably as early as cortical area V1, even when the association between colour and motion is perceptually inaccessible.     

Pattern discrimination after unilateral and bilateral ablation of the occipital lobe in the rabbit

Previous studies in rabbits have shown that a unilateral ablation of the occipital lobe leads to a severe impairment of the ability to discriminate striated patterns. Considerable retraining is required in order to reach the 90% correct level with the eye contralateral to the lesion. In the present study the effects of a unilateral and a bilateral ablation are compared. It is concluded that the rudimentary ability to discriminate patterns with the eye contralateral to a unilateral ablation of the occipital lobe is mediated by the remaining ipsilateral cortical projection and not by subcortical structures.     

Specificity of regions processing biological motion

Using functional magnetic resonance imaging and point light displays portraying six different human actions, we were able to show that several visual cortical regions, including human MT/V5 complex, posterior inferior temporal gyrus and superior temporal sulcus, are differentially active in the subtraction comparing biological motion to scrambled motion. Comparison of biological motion to three-dimensional rotation (of a human figure), articulated motion and translation suggests that human superior temporal sulcus activity reflects the action portrayed in the biological motion stimuli, whereas posterior inferior temporal gyrus responds to the figure and hMT/V5+ to the complex motion pattern present in biological motion stimuli. These results were confirmed with implied action stimuli.     

Morphological damage to the premature fetal rat brain after acute carbon monoxide exposure

For most brain regions the responses of neurons to stimulation of the primary visual cortex (CTX) are unknown. The objective of this study was to determine how neurons (single-unit activity) in major limbic, thalamic, hypothalamic, and visual regions respond to electrical stimulation of the CTX. Cats underwent low cerveau isolé surgery (isolate forebrain) and electrode implantation. Unit activity was analyzed as action potentials recorded extracellularly under control (spontaneous firing rate) and experimental (poststimulus rate) conditions. A total sample of 2055 units were localized anatomically. The effect of CTX stimulation was primarily inhibitory in the initial 500-ms poststimulus responses. Only 20 cells (<1%) showed initial excitatory responses. Highly responsive regions included areas 17, 18, 19 and the hippocampal formation. Subcortical regions which showed marked (P < 0.01) inhibitory responses form part of the ascending reticular system (anterior, intralaminar, and reticular thalamic nuclei, and tegmental nucleus). Similar effects were also observed in the anteromedial hypothalamus. Only two regions showed significant (P < 0.05) prolonged responses (1 to 5 s) to CTX stimuli. One of them, the prostriatal cortex, exhibited increases in firing rates. The other, the cingulate cortex, showed inhibitory initial and prolonged responses. Therefore, information provided by CTX stimulation is distributed to different limbic and subcortical targets. We suggest that the mechanisms responsible for the effects of visual stimuli on arousal and emotion may be mediated by inhibition of ascending reticular pathways.     

Breaking camouflage: responses of neurons in the middle temporal area to stimuli defined by coherent motion

Camouflaged animals remain inconspicuous only insofar as they remain static. This demonstrates that motion is a powerful cue for figure-ground segregation, allowing detection of moving objects even when their luminance and texture characteristics are matched to the background. We investigated the neural processes underlying this phenomenon by testing the responses of neurons in the middle temporal area (MT) to 'camouflaged' bars, which were rendered visible by motion. These responses were compared with those elicited by 'solid' bars, which also differed from background in terms of their mean luminance. Most MT neurons responded strongly to camouflaged bars, and signaled their direction of motion with precision, with direction-tuning curves being only slightly wider than those measured with solid bars. However, the tuning of most MT cells to stimulus length and speed depended on the type of stimulus - in comparison with solid bars, responses to camouflaged bars typically showed more extensive length summation, weak end-inhibition, and stronger attenuation at high speeds. Moreover, the emergence of direction selectivity was delayed in trials involving camouflaged bars, relative to solid bars. Comparison with results obtained in the first (V1) and second (V2) visual areas, using similar stimuli, indicates that neural computations performed in MT result in significantly stronger and more accurate signals about camouflaged objects, particularly in situations in which these are relatively large and slow moving. These computations are likely to represent an important step in enabling cue-invariant perception of moving objects, particularly in biologically relevant situations.     

Visual discrimination after bilateral removal of the visual cortex in the rabbit

Rabbits were trained on a brightness and a vertical vs horizontal discrimination. After bilateral removal of the visual cortex the threshold of brightness discrimination was significantly higher. In addition, there was a severe impairment of striated pattern discrimination.     

Perception of emotions from faces and voices following unilateral brain damage

The importance of the right hemisphere in emotion perception in general has been well documented but its precise role is disputed. We compared the performance of 30 right hemisphere damaged (RHD) patients, 30 left hemisphere damaged (LHD) patients, and 50 healthy controls on both facial and vocal affect perception tasks of specific emotions. Brain damaged subjects had a single episode cerebrovascular accident localised to one hemisphere. The results showed that right hemisphere patients were markedly impaired relative to left hemisphere and healthy controls on test performance: labelling and recognition of facial expressions and recognition of emotions conveyed by prosody. This pertained at the level of individual basic emotions, positive versus negative, and emotional expressions in general. The impairment remained highly significant despite covarying for the group's poorer accuracy on a neutral facial perception test and identification of neutral vocal expressions. The LHD group were only impaired relative to controls on facial emotion tasks when their performance was summed over all the emotion categories and before age and other cognitive factors were taken into account. However, on the prosody test the LHD patients showed significant impairment, performing mid-way between the right hemisphere patients and healthy comparison group. Recognition of positive emotional expressions was better than negative in all subjects, and was not relatively poorer in the LHD patients. Recognition of individual emotions in one modality correlated weakly with recognition in another, in all three groups. These data confirm the primacy of the right hemisphere in processing all emotional expressions across modalities--both positive and negative--but suggest that left hemisphere emotion processing is modality specific. It is possible that the left hemisphere has a particular role in the perception of emotion conveyed through meaningful speech.     

Visual detection of motion speed in humans: spatiotemporal analysis by fMRI and MEG

Humans take a long time to respond to the slow visual motion of an object. It is not known what neural mechanism causes this delay. We measured magnetoencephalographic neural responses to light spot motion onset within a wide speed range (0.4-500 degrees /sec) and compared these with human reaction times (RTs). The mean response latency was inversely related to the speed of motion up to 100 degrees /sec, whereas the amplitude increased with the speed. The response property at the speed of 500 degrees /sec was different from that at the other speeds. The speed-related latency change was observed when the motion duration was 10 msec or longer in the speed range between 5 and 500 degrees /sec, indicating that the response is directly related to the speed itself. The source of the response was estimated to be around the human MT+ and was validated by functional magnetic imaging study using the same stimuli. The results indicate that the speed of motion is encoded in the neural activity of MT+ and that it can be detected within 10 msec of motion observation. RT to the same motion onset was also inversely related to the speed of motion but the delay could not be explained by the magnetic response latency change. Instead, the reciprocal of RT was linearly related to the reciprocal of the magnetic response latency, suggesting that the visual process interacts with other neural processes for decision and motor preparation.     

When transcranial magnetic stimulation (TMS) modulates feature integration

How the brain integrates visual information across time into coherent percepts is an open question. Here, we presented two verniers with opposite offset directions one after the other. A vernier consists of two vertical bars that are horizontally offset. When the two verniers are separated by a blank screen (interstimulus interval, ISI), the two verniers are perceived either as two separate entities or as one vernier with the offset moving from one side to the other depending on the ISI. In both cases, their offsets can be reported independently. Transcranial magnet stimulation (TMS) over the occipital cortex does not interfere with the offset discrimination of either vernier. When a grating, instead of the ISI, is presented, the two verniers are not perceived separately anymore, but as 'one' vernier with 'one' fused vernier offset. TMS strongly modulates the percept of the fused vernier offset even though the spatio-temporal position of the verniers is identical in the ISI and grating conditions. We suggest that the grating suppresses the termination signal of the first vernier and the onset signal of the second vernier. As a consequence, perception of the individual verniers is suppressed. Neural representations of the vernier and second vernier inhibit each other, which renders them vulnerable to TMS for at least 300 ms, even though stimulus presentation was only 100 ms. Our data suggest that stimulus features can be flexibly integrated in the occipital cortex, mediated by neural interactions with outlast stimulus presentations by far.     

新生大鼠缺氧缺血性脑损伤后CIRP表达与意义

目的观察新生大鼠缺氧缺血性脑损伤(HIBD)后冷诱导RNA结合蛋白(CIRP)表达的变化情况。方法将40只7日龄新生SD大鼠随机分为假手术组和HIBD组,分别采用real-time PCR及免疫组织化学方法检测假手术组和HIBD后不同时间点(6、12、24和48h)CIRP在大鼠脑皮质与海马表达的变化。结果利用免疫组化和real-time PCR检测发现,大鼠脑皮质的CIRP蛋白和CIRP mRNA表达呈持续降低趋势,HIBD后6、12 h开始减少;24~48h下降更为明显。海马CIRP蛋白和CIRP mRNA表达则表现为6 h先升48h后降。结论CIRP参与了新生大鼠脑缺氧缺血的应激过程,可能与缺氧缺血性脑损伤后的脑水肿及神经元凋亡相关。     

Repair process of fetal brain after 5-azacytidine-induced damage

The fetal brain is susceptible to many extrinsic stresses. Some of these stresses induce excessive cell death in the prenatal stage, leading to anomalies in the neonatal brain. However, it is unclear how the developing brain responds to and repairs the prenatal tissue damage. We treated pregnant rats on day 13 of gestation with 5-azacytidine, one of the compounds that induces excessive cell death and inhibits proliferation in neural progenitor cells, to damage the fetal brain, and investigated the repair process up to 60 h after treatment. Histological analysis showed that 5-azacytidine induced strong apoptosis of neural cells. By 60 h, apoptotic cells disappeared and the tissue was repaired, although the telencephalic wall remained thinner than in controls. Flow cytometry analysis showed that the cell cycle distribution also returned to control levels at 60 h, suggesting that the repair process was completed around 60 h. During the repair period, amoeboid microglia infiltrated the brain and ingested the apoptotic cells. These microglial cells were positive for the multiple microglial markers, and mRNAs for the microglia-related cytokines tumor necrosis factor alpha, interleukin 1beta and macrophage colony stimulating factor (M-CSF) were up-regulated. DNA microarray analysis showed the up-regulation of genes relevant to glial cells, inflammation, the extracellular matrix, glycolysis, proliferation and neural development. We show here that the developing brain has the capacity to respond to the damage induced by extrinsic chemical stresses, including changing the expression of numerous genes and the induction of microglia to aid the repair process.     

Brain activation associated with visual motion studied by functional magnetic resonance imaging in humans

Localized brain activation in response to moving visual stimuli was studied by functional magnetic resonance imaging (fMRI). Stimuli were 100 small white dots randomly arranged on a visual display. During the Motion condition, the dots moved along random, noncoherent linear trajectories at different velocities. During the Blink condition, the dots remained stationary but blinked on and off every 500 ms. The Motion and Blink conditions continuously alternated with 10 cycles per run and 6–8 runs per experiment. In half of the runs, the starting stimulus condition was Motion, while in the remaining runs it was Blink. A series of 128 gradient echo echoplanar images were acquired from 5–7 slices during each run using a 1.5 T GE Signa with an Advanced NMR echoplanar subsystem. The time series for each voxel were analyzed in the frequency domain. Voxels which demonstrated a significant spectral peak at the alternation frequency and whose phase changed in response to stimulus order were considered activated. These activated voxels were displayed upon high resolution anatomical images to determine the sites of activation and were also transformed into the coordinates of Talairach and Tournoux ([1988] Co-planar Stereotaxic Atlas of the Human Brain, New York: Thieme) for comparison to prior neuroimaging studies. Seven of ten subjects showed clusters of activation bilaterally at the junction of the temporal and occipital lobes (area 37) in response to moving stimuli. Most activated voxels were located within or adjacent to a region designated the parietal-temporal-occipital fossa, or PTOF. Five subjects also showed activation to moving stimuli in midline occipital cortex. The activated voxels in midline cortex had a significantly shorter phase delay in their MR signal change relative to voxels in PTOF. © 1995 Wiley-Liss, Inc. 1

1 This article is a US Government work and, as such, is in the public domain in the United States of America

     

The locus of the posterior subdivision of the inferotemporal visual learning area in the monkey

In an attempt to define the posterior subdivision of the inferotemporal visual learning area more precisely than before, pattern discrimination retention, serial object discrimination learning and concurrent object discrimination learning were tested in 16 monkeys with lesions in one of four different cytoarchitectural areas; TEO, OA, OB and OC, and in five unoperated monkeys. Marked impairment was found only in pattern discrimination retention and only in the monkeys with lesions of area TEO. It was concluded that the posterior limit of the inferotemporal visual learning area is at the ascending limb of the inferior occipital sulcus, and that the posterior subdivision thus comprises the single anatomical area TEO and does not extend into areas OA and OB.     

3D left hyperschematia after right brain damage

ABSTRACT

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves the motor symptoms of Parkinson’s disease (PD). The STN may represent an important relay station not only in the motor but also the associative cortico-striato-thalamocortical pathway. Therefore, STN stimulation may alter cognitive functions, such as working memory (WM). We examined cortical effects of STN-DBS on WM in early PD patients using functional near-infrared spectroscopy. The effects of dopaminergic medication on WM were also examined. Lateral frontal activity during WM maintenance was greater when patients were taking dopaminergic medication. STN-DBS led to a trend-level worsening of WM performance, accompanied by increased lateral frontal activity during WM maintenance. These findings suggest that STN-DBS in PD might lead to functional modifications of the basal ganglia-thalamocortical pathway during WM maintenance.     

Pattern motion selectivity in population responses of area 18

It is commonly believed that the complexity of visual stimuli represented by individual neurons increases towards higher cortical areas. However, even in early visual areas an individual neuron's response is influenced by stimuli presented outside its classical receptive field. Thus, it has been proven difficult to characterize the coding of complex stimuli at the level of single neurons. We therefore investigated population responses using optical imaging in cat area 18 to complex stimuli, plaids. Plaid stimuli are composed of two superimposed gratings moving in different directions. They may be perceived as either two separate surfaces or as a global pattern moving in intermediate direction to the components' direction of motion. We found that in addition to activity maps representing the individual components' motion, plaid stimuli produced activity distributions matching the predictions from a pattern-motion model in central area 18. Thereby, relative component- and pattern-like modulations followed the degree of psychophysical pattern bias in the stimulus. Thus, our results strongly indicate that area 18 exhibits a substantial response to pattern-motion signals at the population level suggesting the presence of intrinsic or extrinsic mechanisms that allow for integration of motion responses from far outside the classical receptive field.