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It is now well established that the human brain is endowed with a mechanism that pairs action perception with its execution. This system has been extensively studied using visual stimuli and recent evidence suggests that it is also responsive to the sound of motor actions. Here, we presented action (finger and tongue clicks) and acoustically matched sounds to investigate action-related sound processing in a 12-year-old child undergoing intracranial monitoring of epileptic seizures. Electroencephalography grids were located over a large portion of the right hemisphere, including motor cortex. Wavelet analysis carried out on electrodes overlying the functionally defined hand representation of the motor cortex revealed early (100 ms) and late (250–450 ms) decreases in mu rhythm power (12 and 20 Hz) selective for natural finger-clicks compared with control sounds. These data suggest the presence of a rapid, multimodal resonance mechanism modulating motor cortex activity.

It has been proposed that the corpus callosum may play an important role in spectral cue processing that allows vertical auditory movement perception. The purpose of the present study was to assess the contribution of the corpus callosum to this type of auditory processing. Noise bursts were presented to 10 control and two callosal agenesis individuals from different positions located within midsagittal and coronal planes. Although acallosal participants were comparable with controls in their ability to correctly identify the trajectory direction or its length, they showed greater capability in detecting motion per sewhen the task was difficult. These results suggest that in the absence of the corpus callosum, compensatory reorganization of the brain allowed for superior auditory spectral cue processing.

Event-related potentials in the form of mismatch negativity were recorded to investigate auditory scene analysis capabilities in a person with a very circumscribed haemorrhagic lesion at the level of the right inferior colliculus. The results provide the first objective evidence that processing at the level of the inferior colliculus plays an important role in human auditory frequency discrimination. Moreover, the electrophysiological data suggest that following this unilateral lesion, the auditory pathways fail to reorganize efficiently.

Multisensory integration can occur at relatively low levels within the central nervous system. Recent evidence suggests that multisensory audio-visual integration for speech may have a subcortical component, as acoustic processing in the human brainstem is influenced by lipreading during speech perception. Here, stimuli depicting the McGurk illusion (a demonstration of auditory–visual integration using speech stimuli) were presented to a 12-year-old child (FX) with a circumscribed unilateral lesion of the right inferior colliculus. When McGurk-type stimuli were presented in the contralesional hemifield, illusory perception reflecting bimodal integration was significantly reduced compared with the ipsilesional hemifield and a group of age-matched controls. These data suggest a functional role for the inferior colliculus in the audio-visual integration of speech stimuli.

The current experiment examined the importance of visual input on the construction of inner spatial representations. Early and late-onset blind and paired control participants performed a tactile spatial orientation task. No significant group differences were observed, indicating that the blind can represent space. More errors, however, were committed by the early blind than by the late blind and sighted individuals in portions of the task that involved mental rotation skills, suggesting a potential facilitating role for vision in the proper development of spatial constructs.

Individuals deprived of vision early in life often demonstrate exceptional abilities in their remaining sensory modalities in order to compensate for their handicap. Recent studies have shown that some of these abilities also extend to those who have lost their sight later in life. It is not clear, however, what mechanisms underlie these abilities. Here, we examined cortical activation using positron emission tomography in late-onset blind participants during a free-field auditory localization task. Even though no behavioral enhancements were observed in this testing condition relative to sighted controls, the results revealed that the occipital cortex was nonetheless activated during task execution. We conclude that late-onset blind individuals do manifest cerebral reorganization, although its functional relevance to the task is less clear.

The visual processing of radially modulated concentric patterns was studied in human participants, aged 3–22 years, by recording event-related potentials. These stimuli are known to activate the fusiform face area as well as area V4 in normal adults. The electrophysiological data showed a P1 latency that reached a maturation asymptote before 3 years of age, whereas that of N1 and P2 became adultlike by 13 years of age. In addition, the distribution of the P2 component over the scalp was focalized in the primary visual cortex before adolescence and became distributed over the entire brain after adolescence. Radially modulated concentric stimuli thus induce brain activation that is not mature until 13 years of age.

The degree of involvement of the right and left hemispheres in the system matching perception and execution of actions remains unclear. Some studies have proposed that action observation involves a bilateral network of brain areas, whereas others have suggested left-hemisphere dominance. We explored hemispheric lateralization associated with action observation using transcranial magnetic stimulation over primary motor cortex devoid of callosal influences. We assessed corticospinal excitability related to observation of finger movements in one split-brain patient and six controls. Results revealed that the left hemisphere of the split-brain patient shows enhanced excitability during action observation, whereas no enhancement was found in the right hemisphere. The controls showed increased excitability in both hemispheres during action observation. Our findings suggest a left-hemisphere dominance for mirror-neuron function in the absence of a corpus callosum.

We have used event-related potentials (ERP) to assess cerebral activity following mild traumatic brain injuries in 20 college athletes practising contact sports. Concussion victims showed a striking decrease in P300 amplitude, an effect presumed to reflect alterations in attentional-cognitive processes. Moreover, the degree of impairment was strongly related to the severity of post-concussion symptoms. Our data suggest that concussions cause objectively measurable changes in the electro-physiological markers of brain activity and hence in the functions of the structures from which they originate. ERPs may thus constitute a reliable method to accurately monitor the clinical course and recovery of head injuries in athletes.

To identify cortical structures that subserve residual motor and sensory function in patients with congenital hemiparesis due to a porencephalic cyst, we examined, using [15O]H2O, PET and somatosensory evoked potentials (SEPs) in three patients with left-sided hemiparesis who had undergone hemispherectomy. Motor stimulation of the affected hand produced ipsilateral activation in the premotor area in all patients, the SMA in two patients, and SII in two patients. Vibrotactile stimulation resulted in activation of the ipsilateral SII in all subjects. Median nerve stimulation of the affected hand produced ipsilateral long-latency SEPs in fronto-centro-parietal areas, whereas stimulation of the non-affected hand produced normal early cortical potentials in the contralateral hemisphere. Our results suggest that residual function in the paretic hand is warranted through non-primary motor and sensory areas, and higher order associative areas in the intact hemisphere.

Transcranial magnetic stimulation (TMS) studies have suggested that callosal afferents may mediate inhibition of the ipsilateral motor cortex (IMC) during unilateral hand movements. To test this concept, we used fMRI to determine whether acallosal patients have increased IMC activation with either complex or simple unilateral finger movements. Neither the localization of motor cortical regions activated, the volumes of activation, or the relative hemispheric lateralization of activations were different between the patients and normal controls. The potential callosal inhibitory pathway identified by TMS therefore does not appear to contribute to the interhemispheric suppression of physiologically relevant activations in the motor cortex as measured by fMRI.

Visually challenged individuals often compensate for their handicap by developing supra-normal abilities in their remaining sensory systems. Here, we examined the scalp distribution of components N1 and P3 of auditory evoked potentials during a sound localization task in four totally blind subjects who had previously shown better performance than sighted subjects. Both N1 and P3 waves peaked at their usual positions while blind and sighted individuals performed the task. However, in blind subjects these two components were also found to be robust over occipital regions while in sighted individuals this pattern was not seen. We conclude that deafferented posterior visual areas in blind individuals are recruited to carry out auditory functions, enabling these individuals to compensate for their lack of vision.