Short-term crossmodal plasticity of the auditory steady-state response in blindfolded sighted individuals

This study investigated the effect of short-term visual deprivation on auditory steady-state response (ASSR) to amplitude-modulated tones. Magnetoencephalography data were acquired while subjects performed an auditory detection task under both monaural and dichotic presentation conditions. Analyses were performed on the spectral power, mean amplitudes and dipole positions of the ASSR at the onset of blindfolding, as well as after 2, 4 and 6 h of visual deprivation. Results show a modulation of the spectral power of the ASSR at the frequencies that were present in the stimulus after 6 h of sensory deprivation, and this was especially true for the dichotic condition. Moreover, participants showed two spectral peaks in the occipital cortex at the end of the visual deprivation period, a phenomenon normally observed in the auditory cortex. Our results shed light not only on the timeline associated with short-term crossmodal recruitment of input-deprived sensory cortices but also demonstrate that the visual cortex can display auditory cortex-like functioning in response to the ASSR. Importantly, our results also highlight the importance of taking into consideration individual differences when investigating crossmodal plastic phenomena. Indeed, the occipital spectral peaks were only observed in half the subjects following short-term deprivation.     

A Long-Term Observation on a Case of Epilepsy with Occipital Continuous Spikes

Abstract: We have reported a 38-year-old female who did not show clinical seizures during continuous spikes in the left occipital area over a period of 18 : years. As to the neurological findings, visual disturbance, optic nerve atrophy and right hemianopsia were almost always present. The low density area distributing f'rom the left occipital area to the left temporal one on the CT revealed to be porencephaly. From the clinical Andings obtained in this case, the lesion responsible for the occipital continuom spikes could be ascribed to be functional abnormality of the visual pathway connecting the left lateral geniculate body with the left occipital cortex.     

The physiological basis of visual hallucinations after damage to the primary visual cortex

We used functional magnetic resonance imaging to examine the neuroanatomical correlates of visual hallucinations in a patient with a left visual field defect who had suffered bilateral occipital infarction. By cross-correlating the functional magnetic resonance imaging data with the hallucination events, we were able to identify the cerebral activity underlying the hallucinations. Bilateral activation was observed during visual stimulation in the calcarine fissure and the same activation was found medially in the left and right occipital cortex adjacent to the infarcted areas. This pattern of perilesional visual cortex activation is consistent with the suggestion that primary sensory areas may be involved in visual hallucinations after stroke.     

The cortical representation of foveal stimuli: evidence from quadrantanopia and TMS-induced suppression

To address the extent to which the visual foveal representation is split, we examined a 29-year-old patient with a lower right quadrantanopia following surgical removal of the left occipital cortex above the calcarine sulcus and compared her performance with subjects receiving transcranial magnetic stimulation (TMS) over the occipital lobes. In a letter/digit classification task, the patient responded accurately to targets presented in the upper visual field, for all horizontal eccentricities. In the lower visual field, she failed to discriminate letters from digits when targets were presented in the right, but not the left visual field (RVF and LVF, respectively). This pattern was also true for the foveal targets, with poor performance to foveal-RVF (0.5 degrees to the right of fixation) but not foveal-LVF (0.5 degrees to the left of fixation) targets. Similar patterns of normal performance to LVF but not RVF or foveal-RVF targets were observed in a group of nine normal observers when TMS was applied over their left occipital cortex. Complementary impairments to LVF and foveal-LVF target classification were induced with TMS over the right occipital cortex. Thus, we have induced an hemianopic pattern in normal observers contralateral to the magnetically stimulated hemisphere. This correspondence between real and TMS-induced visual field defects is further evidence, in neurologically intact subjects, that the cortical representation of the fovea is split between the two hemispheres along the vertical meridian.     

Backward masked fearful faces enhance contralateral occipital cortical activity for visual targets within the spotlight of attention

Spatial attention has been argued to be adaptive by enhancing the processing of visual stimuli within the ‘spotlight of attention’. We previously reported that crude threat cues (backward masked fearful faces) facilitate spatial attention through a network of brain regions consisting of the amygdala, anterior cingulate and contralateral visual cortex. However, results from previous functional magnetic resonance imaging (fMRI) dot-probe studies have been inconclusive regarding a fearful face-elicited contralateral modulation of visual targets. Here, we tested the hypothesis that the capture of spatial attention by crude threat cues would facilitate processing of subsequently presented visual stimuli within the masked fearful face-elicited ‘spotlight of attention’ in the contralateral visual cortex. Participants performed a backward masked fearful face dot-probe task while brain activity was measured with fMRI. Masked fearful face left visual field trials enhanced activity for spatially congruent targets in the right superior occipital gyrus, fusiform gyrus and lateral occipital complex, while masked fearful face right visual field trials enhanced activity in the left middle occipital gyrus. These data indicate that crude threat elicited spatial attention enhances the processing of subsequent visual stimuli in contralateral occipital cortex, which may occur by lowering neural activation thresholds in this retinotopic location.     

纯失读症与大脑半球枕叶病变的关系

目的 探讨纯失读症与大脑半球枕叶病变的关系。方法 分析3例左枕叶梗死和2例右枕叶梗死患者的语言功能，详细阅读及视空间，忽视功能检查和影像学检查资料。结果 3例在枕叶梗死患者中，2例表现失读不伴失定，1例表现失读伴失写，阅读检查各自有其特点，并与病变的部位和范围密切相关；2例右枕叶梗死患者，语言功能无异常，表现视空间功能障碍。结论 大脑半球的左右枕叶分别对文字阅读和视空间结构功能有明显的侧向分化特点，枕叶皮层对各种视觉的语言符号存在着相对分化的阅读中枢或相对独立的阅读系统。     

The effect of bilateral visual cortex lesions on the development of eye movements and perception

We studied the eye movements and visual perception in a man with extensive bilateral occipital lesions acquired at birth. He had 3/500 acuity, limited visual fields, and extrafoveal fixation attributable to an intact left superior visual cortex. Analysis of digitized electro-oculography and magnetic search coil data showed normal saccade dynamics. He could make voluntary saccades. Smooth pursuit of suprathreshold targets was mostly saccadic and did not improve with added nonvisual cues. Our results support the hypothesis that the visual cortex is crucial to the development of eye movements. The foveal representation in the occipital lobes, missing in this subject, is needed for development of normal smooth pursuit.     

Palinopsia and perilesional hyperperfusion following subcortical hemorrhage

We report a patient who exhibited transient palinopsia and visual hallucinations. Disturbances initially included an auditory component and increasingly were localized to the left visual field. These events occurred during recovery from a right subcortical hematoma with left homonymous hemianopia. Single-photon emission computed tomography (SPECT) demonstrated extensive perilesional hyperperfusion involving parts of the right parietal, temporal, and occipital cortex. Perilesional hyperperfusion disappeared as the visual abnormalities diminished. We believe that excitatory neuronal activation in perilesional cortex during recovery contributed importantly to the transient abnormal perceptions.     

Ictal visual hallucination intermittent photic stimulation: using evaluation of the clinical findings, ictal EEG, ictal SPECT, and rCBF]

A 43-year-old, right-handed woman experienced right hand paresthesias and a visual field abnormality. We attributed her symptoms to psychiatric abnormalities, due to the presence of delusions and auditory hallucinations. Upon photostimulation, she experienced left visual field hallucinations and demonstrated slow waves on the right parieto-occipital regions. The clinical and electro-encephalographic findings suggested that these episodes were epileptic seizures originating from the right occipital region. Ictal fear appeared at the end of the seizure, reflecting the spread of seizure activity to the mesial temporal region. Ictal SPECT images showed hyper-perfusion in the right occipital region and left cerebellar cortex. rCBF in the occipital lobe was significantly asymmetrical. When we encounter an epileptic patient with psychosis who has a visual hallucination, we should consider the possibility of epileptic seizure originating from the occipital lobe.     

A case of visual perseveration attack caused by transverse-sigmoid sinus dural arteriovenous fistula]

A case of visual perseveration attack in the right superior quadrantic visual field caused by left transverse-sigmoid sinus dural arteriovenous fistula (AVF) was reported. A 75-year old right-handed man noticed that when he saw an object, the image sometimes persisted even after he looked away or the object was removed. The palinoptic images always appeared in the right superior quadrant visual field, consisted of a row of multiple objects all identical to the real one in shape, and were accompanied by photopsia. The palinoptic images disappeared within a few minutes. He was neurologically normal and showed no hemianopia or quadrantanopia on admission. EEG showed no epileptic discharge. CT scanning of the brain revealed a small high density area in the left occipital lobe. MRI demonstrated hyperintensity in the left inferior occipital lobe corresponding to the lower part of Brodmann's areas 18 and 19 on T2 weighted image and flow-voids caused by the dilated left occipital artery. 99mTc-ECD SPECT disclosed a decrease of regional cerebral blood flow in the left occipital lobe. Cerebral angiography revealed dural AVF fed by three branches of the left occipital artery and another branch of the left ascending pharyngeal artery with retrograde drainage into the left transverse sinus, sigmoid sinus, and dilated cortical veins. The left transverse and sigmoid sinuses were occluded. Visual perseveration disappeared following the treatment of the dural AVF by transarterial embolization. Because the lesions on MRI and SPECT improved after the treatment, these lesions were considered to represent not infarction but vasogenic edema due to venous congestion. We emphasized the role of the left inferior occipital lesion including the secondary visual cortex (Brodmann's areas 18 and 19) as the cause of visual perseveration in the right superior quadrantic visual field.     

Neural mechanism of reading]

We conducted positron emission tomography studies on reading and found that two distinct areas were activated, i.e. the left fusiform/inferior temporal gyri (posterior inferior temporal cortex, Area 37) by kanji words and the fusiform/inferior occipital gyri (posterior occipital gyri, Area 18/19) by kana words. Clinically, alexia and agraphia for kanji is caused by a posterior inferior temporal cortex lesion. Moreover, pure alexia more impaired for kanji results from a fusiform gyrus lesion, whereas pure alexia for kana occurs because of damage to the posterior occipital gyri. These experimental and clinical findings suggest that impaired letter identification in Area 18/ 19 causes pure alexia for kana, disrupted visual images of words in Area 37 results in alexia with agraphia for kanji, and impaired access to the visual image storage (Area 37) yields pure alexia dominantly disturbed for kanji.     

The neuroanatomy of visual enumeration: differentiating necessary neural correlates for subitizing versus counting in a neuropsychological voxel-based morphometry study

This study is the first to assess lesion-symptom relations for subitizing and counting impairments in a large sample of neuropsychological patients (41 patients) using an observer-independent voxel-based approach. We tested for differential effects of enumerating small versus large numbers of items while controlling for hemianopia and visual attention deficits. Overall impairments in the enumeration of any numbers (small or large) were associated with an extended network, including bilateral occipital and fronto-parietal regions. Within this network, severe impairments in accuracy when enumerating small sets of items (in the subitizing range) were associated with damage to the left posterior occipital cortex, bilateral lateral occipital and right superior frontal cortices. Lesions to the right calcarine extending to the precuneus led to patients serially counting even small numbers of items (indicated by a steep response slope), again demonstrating an impaired subitizing ability. In contrast, impairments in counting large numerosities were associated with damage to the left intraparietal sulcus. The data support the argument for some distinctive processes and neural areas necessary to support subitization and counting with subitizing relying on processes of posterior occipital cortex and with counting associated with processing in the parietal cortex.     

Cortico-cortical evoked potentials and stimulation-elicited gamma activity preferentially propagate from lower- to higher-order visual areas

ObjectiveThe lower-order visual cortex in the medial–occipital region is suggested to send feed-forward signals to the higher-order visual cortex including ventral–occipital–temporal and dorsal–occipital regions. We determined how stimulation-elicited cortical-signals propagate between lower- and higher-order visual cortices, and whether the magnitudes of stimulation-elicited cortical-signals recorded in the higher-order visual cortex differed from those recorded in the lower-order one.MethodsWe studied 10 patients with focal epilepsy who underwent extraoperative electrocorticography recording. Trains of 1-Hz stimuli with an intensity of 3 mA were delivered to an electrode pair within the medial–occipital region; then, cortico-cortical evoked-potential (CCEP) and stimulation-elicited gamma-activity at 80–150 Hz were measured in the ventral–occipital–temporal and dorsal–occipital regions. Likewise, CCEP and stimulation-elicited gamma-activity, driven by stimuli within the higher-order visual cortex, were measured in the lower-order visual cortex.ResultsCCEPs generated, via feed-forward propagations, in the higher-order visual cortex were significantly larger than those generated, via feed-back propagations, in the lower-order visual cortex. Stimulation of the lower-order visual cortex elicited augmentation of gamma-activity in the higher-order visual cortex after the preceding CCEP subsided.ConclusionThe propagation manners of stimulation-elicited cortical-signals differ between feed-forward and feed-back directions in the human occipital lobe.Significance:Such difference may need to be taken into consideration for future clinical application of CCEPs and stimulation-elicited gamma-augmentation in presurgical evaluation for epilepsy surgery.     

A case of naturally occurring visual field loss in a chimpanzee with an arachnoid cyst

Deficits in the occipital cortex have varying consequences among mammalian species. Such variations are indicative of evolutionary transitions in the striate cortical contribution to visually guided behavior. However, little is known about the role of the striate cortex in visually guided behavior in chimpanzees due to ethical concerns about invasive experiments and methodological limitations such as the inability to monitor gaze movements. We had the opportunity to study the behavioral consequences of a deficit in the occipital cortex in a chimpanzee with a naturally occurring arachnoid cyst in her right occipital lobe. We assessed the chimpanzee's ability to detect a small light probe (0.5 visual degree, Michelson contrast>0.9) presented at several locations in the visual field while monitoring gaze direction using an infra-red remote eye-tracker recently introduced to studies of great apes. The results showed the chimpanzee was unable to detect the probe in the lower left quadrant of the visual field, suggesting severe loss of contrast sensitivity in a part of hemivisual field that is retinotopically corresponded to the hemisphere of the cyst. A chimpanzee with a naturally occurring deficit in the right striate cortex and the availability of remote eye-tracking technology presented a unique opportunity to compare the role of the occipital lobe in visually guided behavior among various primate species.     

Alexia without agraphia, hemianopia, or color-naming defect: a disconnection syndrome.

A patient with alexia without agraphia, hemianopia, or color-naming defect was found at operation to have a meningioma arising from the tentorium cerebelli that compressed the inferior aspect of the left temporal-occipital junction. It is presumed to have involved only the left ventral visual association cortex and its inferior outflow tracts to the angular gyrus. The input from the right occipital area also was disconnected from the visual language verbal association area by involvement of the ventral outflow of the splenium of the corpus callosum. Preservation of color naming and matching suggests that these functions are dependent on the integrity of more dorsal occipital association systems.     

Colour anomia restricted to the left visual hemifield after splenial disconnexion.

In a patient with damage to the right occipital lobe and to the splenium of the corpus callosum, an incomplete colour anopia in the left upper quadrants and a colour anomia was found for the complete left visual hemifield beyond 2 degrees eccentricity. The patient had no difficulty in recognising coloured targets when presented in the periphery of the left visual hemifield and in the foveal region, but could not name them correctly. The results suggest that the lesion of the splenium of the corpus callosum disconnects the right visual cortex from the language areas of the left hemisphere, and the specific disturbance of colour naming is the consequence.     

Developmental lesions of visual cortex influence control of reaching

We examined visually guided reaching movements in a young adult (EW) who had extensive bilateral lesions in the visual cortex since birth. EW lacked a right occipital lobe and ventral portions of the left and had poor visual acuity (3/400), yet could point to visual targets as quickly as 9 controls with visual cortex lesions acquired in adulthood and 4 adults without neurological disease. However, EW's endpoint variability and hand movement path curvature were much greater, especially for left hand movements, in concert with large sensorimotor transformation errors. Experimental reduction of acuity (to 3/240 or worse) in the normal controls produced symmetric increases in endpoint variability but did not change hand path curvature, indicating that EW's impaired movements were not due to poor vision alone. Results suggest that visual cortex in early life supports the development of lifelong neural mechanisms for the planning and control of reaching movements.     

Impaired reading in patients with right hemianopia

A left occipital stroke may result in alexia for two reasons, which may coexist depending on the distribution of the lesion. A lesion of the left lateroventral prestriate cortex or its afferents impairs word recognition ("pure" alexia). If the left primary visual cortex or its afferents are destroyed, resulting in a complete right homonymous hemianopia, rightward saccades during text reading are disrupted ("hemianopic" alexia). By using functional imaging, we showed two separate but interdependent systems involved in reading. The first, subserving word recognition, involved the representation of foveal vision in the left and right primary visual cortex and the ventral prestriate cortex. The second system, responsible for the planning and execution of reading saccades, consisted of the representation of right parafoveal vision in the left visual cortex, the bilateral posterior parietal cortex (left > right), and the frontal eye fields (right > left). Disruption of this distributed neural system was demonstrated in patients with severe right homonymous hemianopia, commensurate with their inability to perform normal reading eye movements. Text reading, before processes involved in comprehension, requires the integration of perceptual and motor processes. We have demonstrated these distributed neural systems in normal readers and have shown how a right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading.     

Distorted images of one's own body activates the prefrontal cortex and limbic/paralimbic system in young women: a functional magnetic resonance imaging study.

BACKGROUND: Our aim was to study the gender differences in brain activation upon viewing visual stimuli of distorted images of one's own body. METHODS: We performed functional magnetic resonance imaging on 11 healthy young men and 11 healthy young women using the "body image tasks" which consisted of fat, real, and thin shapes of the subject's own body. RESULTS: Comparison of the brain activation upon performing the fat-image task versus real-image task showed significant activation of the bilateral prefrontal cortex and left parahippocampal area including the amygdala in the women, and significant activation of the right occipital lobe including the primary and secondary visual cortices in the men. Comparison of brain activation upon performing the thin-image task versus real-image task showed significant activation of the left prefrontal cortex, left limbic area including the cingulate gyrus and paralimbic area including the insula in women, and significant activation of the occipital lobe including the left primary and secondary visual cortices in men. CONCLUSIONS: These results suggest that women tend to perceive distorted images of their own bodies by complex cognitive processing of emotion, whereas men tend to perceive distorted images of their own bodies by object visual processing and spatial visual processing.     

偏头痛与静息态脑功能连接研究

目的本文研究采用静息态功能磁共振成像(rfMRI)技术描述偏头痛患者静息态脑功能连接改变,为探索偏头痛的发病机制提供影像学资料。方法收集16例偏头痛患者与16例健康对照,采集rfMRI成像,计算低频振幅,找出感兴趣区做功能连接进行统计分析。结果偏头痛患者左侧岛叶、左侧额下回低频振幅显著低于对照组,右侧视觉皮质低频振幅显著高于对照组;以左侧额下回、右侧枕中回为感兴趣区,发现左侧额下回与脑干之间的功能连接增强,与双侧枕叶之间的功能连接减弱;右侧枕中回与双侧楔前叶延伸至扣带回中部区域之间的功能连接增强,与双侧中央前回、双侧缘上回、双侧颞上回及双侧额下回之间的功能连接减弱。结论偏头痛患者无头痛发作时神经元活动强度改变,大脑功能连接异常,这导致大脑整合信息过程改变,并与偏头痛发病相关。