Visual and tactile interhemispheric transfer compared with the method of Poffenberger

In a simple manual reaction time task, reaction times are longer if the responding hand and visual field of the stimulus are contralateral than when the hand and field are ipsilateral. This small crossed vs. uncrossed difference (CUD) has often been attributed to the interhemispheric transmission time incurred when the hemisphere receiving the sensory input is not the one initiating the motor response. We assessed the generality of the visual CUD by comparing it to the CUD for tactile stimuli. Visual and tactile CUDs did not differ significantly in magnitude, and in both modalities the CUD showed a strong asymmetry, with a positive CUD occurring only for the left hand. This outcome indicates that the properties of the visual CUD are not determined by neural pathways, or hemispheric asymmetries, that are specific to the visual system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46538/1/221_2004_Article_1873.pd

The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side

<p>Abstract</p> <p>Background</p> <p>In normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes.</p> <p>Results</p> <p>Subjects with left-sided deafness showed major neurophysiological changes, in the form of a more symmetrical activation pattern over auditory areas in response to non-speech sound and even a significant reversal of the activation pattern in favour of the cortex ipsilateral to the stimulation in response to speech sound. This was observed not only for AEP amplitudes but also for AEP time course. In contrast, no significant changes were reported for late-AEP responses in subjects with right-sided deafness.</p> <p>Conclusion</p> <p>The results show that cortical reorganization induced by unilateral deafness mainly occurs in subjects with left-sided deafness. This suggests that anatomical and functional plastic changes are more likely to occur in the right than in the left auditory cortex. The possible perceptual correlates of such neurophysiological changes are discussed.</p

Time-Warp–Invariant Neuronal Processing

A biophysical mechanism acting in auditory neurons allows the brain to process the high variability of speaking rates in natural speech in a time-warp-invariant manner

TAOK2 Kinase Mediates PSD95 Stability and Dendritic Spine Maturation through Septin7 Phosphorylation

Abnormalities in dendritic spines are manifestations of several neurodevelopmental and psychiatric diseases. TAOK2 is one of the genes in the 16p11.2 locus, copy number variations of which are associated with autism and schizophrenia. Here, we show that the kinase activity of the serine/threonine kinase encoded by TAOK2 is required for spine maturation. TAOK2 depletion results in unstable dendritic protrusions, mislocalized shaft-synapses, and loss of compartmentalization of NMDA receptor-mediated calcium influx. Using chemical-genetics and mass spectrometry, we identified several TAOK2 phosphorylation targets. We show that TAOK2 directly phosphorylates the cytoskeletal GTPase Septin7, at an evolutionary conserved residue. This phosphorylation induces translocation of Septin7 to the spine, where it associates with and stabilizes the scaffolding protein PSD95, promoting dendritic spine maturation. This study provides a mechanistic basis for postsynaptic stability and compartmentalization via TAOK2-Sept7 signaling, with implications toward understanding the potential role of TAOK2 in neurological deficits associated with the 16p11.2 region

Hemispheric asymmetries in cerebral cortical networks

Since the middle of the 19th century it has been recognized that several higher cognitive functions, including language, are lateralized in cerebral cortex. Neuropsychological studies on patients with brain lesions and rapid developments in brain imaging techniques have provided us with an increasing body of data on the functional aspects of language lateralization, but little is known about the substrate on which these specializations are realized. Much attention has been focused on the gross size and shape of cortical regions involved, but recent findings indicate that the columnar and connectional structure within auditory and language cortex in the left hemisphere are distinct from those in homotopic regions in the right hemisphere. These findings concern parameters that are closely linked to the processing architecture within the respective regions. Thus, the comparison of these microanatomical specializations with their respective functional counterparts provides important insights into the functional role of cerebral cortical organization and its consequences for processing of cortical information in the implementation of complex cognitive functions

Atypical Asymmetry for Processing Human and Robot Faces in Autism Revealed by fNIRS

Deficits in the visual processing of faces in autism spectrum disorder (ASD) individuals may be due to atypical brain organization and function. Studies assessing asymmetric brain function in ASD individuals have suggested that facial processing, which is known to be lateralized in neurotypical (NT) individuals, may be less lateralized in ASD. Here we used functional near-infrared spectroscopy (fNIRS) to first test this theory by comparing patterns of lateralized brain activity in homologous temporal-occipital facial processing regions during observation of faces in an ASD group and an NT group. As expected, the ASD participants showed reduced right hemisphere asymmetry for human faces, compared to the NT participants. Based on recent behavioral reports suggesting that robots can facilitate increased verbal interaction over human counterparts in ASD, we also measured responses to faces of robots to determine if these patterns of activation were lateralized in each group. In this exploratory test, both groups showed similar asymmetry patterns for the robot faces. Our findings confirm existing literature suggesting reduced asymmetry for human faces in ASD and provide a preliminary foundation for future testing of how the use of categorically different social stimuli in the clinical setting may be beneficial in this population

Neuropeptide Y immunoreactivity identifies a group of gamma‐type retinal ganglion cells in the cat

Ganglion cells within the cat retina have been traditionally grouped by morphological criteria into three major classes: alpha, beta, and gamma. The gamma‐type cells have been least well characterized, but the available evidence indicates that this class comprises a relatively heterogeneous population of neurons. In the present study we demonstrate that an antibody for neuropeptide Y (NPY) recognizes a subpopulation of about 2,000 gamma‐type ganglion cells. The NPY‐immunoreactive (IR) neurons project to the superior colliculus and to the C layers of the lateral geniculate nucleus as demonstrated by retrograde labeling with fluorescent tracers (fluorogold or rhodamine latex microspheres). Virtually all of these cells disappear following lesions of the optic nerve. The NPY‐IR ganglion cells were identified as gamma cells on the basis of soma size and dendritic branching patterns. The somas of these neurons are small (8–22 μm in diameter), and each cell is characterized by sparsely branching dendritic processes, usually extending into the middle third of the inner plexiform layer, the physiologically defined ON sublamina. These neurons are distributed across the entire retina, with the highest density at the area centralis. Within local regions of the retina, however, there was no indication that the NPY‐IR gamma cells are arrayed in a regular mosaic pattern. These results provide the first evidence that the gamma class of ganglion cells of the cat retina can be subdivided on the basis of immunocytochemical properties. © 1993 Wiley‐Liss, Inc. Copyright © 1993 Wiley‐Liss, Inc

Stereological Assessment of Purkinje Cell Densities in Autism

Autism Spectrum Disorder (ASD) is heterogeneous neurodevelopmental disorder characterized by impairments in social interaction, communication, and is often accompanied by repetitive or stereotyped behaviors. The cerebellum has been previously implicated in ASD and there is mounting evidence to suggest that the cerebellum plays a critical role in the pathophysiology of this disorder. Purkinje cells have been a focus of this research because they form the only output source of the cerebellum and serve to connect many cortical and subcortical regions of the brain. There is ongoing debate surrounding the condition of these cells and the current study aimed to investigate whether there are differences in the density of Purkinje cells in cerebellar lobule VIIIb using Nissl staining and stereological technique. We anticipate that individuals with autism will exhibit a significant decrease in the number of Purkinje cells compared to typical controls