Biomedical subjects

Jacques Pernier

Publications and source records attributed to Jacques Pernier.

5 recordsLinked to original sources

PubMed2005

Localization of human supratemporal auditory areas from intracerebral auditory evoked potentials using distributed source models.

While source localization methods are increasingly developed to identify brain areas underlying scalp electro/magnetoencephalographic data (EEG/MEG), these methods have not yet been used to identify the sources of intracerebral signals which offer highly detailed information. Here, we adapted the minimum current estimates method to intracranial data in order to localize supratemporal sources of intracerebral auditory 1-kHz-tone-evoked potentials occurring within 100 ms after stimulus onset. After an evaluation of localization method and despite inter-subject variability, we found a common spatiotemporal pattern of activities, which involved the first Heschl's gyrus (H1) and sulcus (HS), the Planum Temporale (PT), H2/H3 when present, and the superior temporal gyrus (STG). Four time periods of activity were distinguished, corresponding to the time range of the scalp components P0, Na, Pa/Pb, and N100. The sources of the earliest components P0 (16-19 ms) and Na (20-25 ms) could be identified in the postero-medial portion of HS or H1. Then, several areas became simultaneously active after 25 ms. The Pa/Pb time range (30-50 ms) was characterized by a medio-lateral and postero-anterior propagation of activity over the supratemporal plane involving successively H1/HS, the Planum Temporale, H2/H3 when present, and the STG. Finally, we found to a large extent that the N100 (55-100 ms) involved almost the same areas as those active during the Pa/Pb complex, with a similar propagation of activities. Reconstructing scalp data from these sources on fictive EEG/MEG channels reproduced classical auditory evoked waveforms and topographies. In conclusion, the spatiotemporal pattern of activation of supratemporal auditory areas could be identified on the individual anatomy using current estimates from intracerebral data. Such detailed localization approach could also be used prior to epilepsy surgery to help identify epileptogenic foci and preserve functional cortical areas.

Acoustic Stimulation↗

PubMed2005

Task-dependent activation latency in human visual extrastriate cortex.

Event related potentials (ERPs) were recorded from subjects who had to perform either an identification task or a simple detection task on moving visual stimuli. Results showed that the amplitude of the so-called visual "N1" component was larger for identification than for mere detection, replicating previous data obtained with static stimuli. However, we also found that: (i) the onset, peak and offset latencies of the visual N1 to dynamic stimuli were significantly earlier in the detection task than in the identification task, and (ii) in both conditions, the coordinates of the equivalent current dipoles best explaining the visual N1 component were consistent with those of the human motion visual area MT+/V5 in the extrastriate cortex. Altogether, these results indicate that dynamic stimuli may activate (at least partly) different pathways and processes in extrastriate cortex according to the nature of the task required on these stimuli.

Adult↗

PubMed2002

Early auditory-visual interactions in human cortex during nonredundant target identification.

A common finding of behavioral studies is that objects characterized by redundant multisensory cues are identified more rapidly than the same objects presented in either unimodal condition. In a previous electrophysiological study in humans, we have described a network of crossmodal interactions that could be associated with this facilitation effect [M.H. Giard, F. Peronnet, J. Cogn. Neurosci. 11(5) (1999) 473-490]. Here, we sought to determine whether the recognition of objects characterized by nonredundant bimodal components may still induce crossmodal neural interactions. Subjects had to identify three objects defined either by auditory or visual features alone, or by the combination of nonredundant auditory and visual features. As expected, behavioral measures showed no sign of facilitation in bimodal processing. Yet, event-related potential analysis revealed the existence of early (<200 ms latency) crossmodal activities in sensory-specific and nonspecific cortical areas, that were partly dependent on the sensory dominance of the subjects to perform the task. Comparative analysis of the interaction patterns involved in redundant and nonredundant cue processing provides evidence for the robustness of the principle of crossmodal neural synergy that applies whatever the stimulus content (redundant or nonredundant information), and for the high flexibility of the neural networks of integration that are sensitive both to the nature of the perceptual task and to the sensory skill of the individual in that particular task.

Adult↗

PubMed2002

Simultaneous intracerebral EEG recordings of early auditory thalamic and cortical activity in human.

We describe documented simultaneous intracerebral auditory evoked potentials from the auditory cortex and medial geniculate body (MGB) of a human patient. The MGB response lasted > 300 ms, with an initial negativity at 13.5 ms (N13), two positive peaks P21 and P29, and two broader negativities N50 and N200. P21 and N50 amplitudes were strongest for lowest tone frequencies, suggesting possible MGB tonotopic organization. Thalamic peaks were strongly interlaced with cortical activities recorded in Heschl's gyri before 30 ms: N13 preceded the first cortical component by 3.5 ms, then P21 and P29 preceded and lagged, respectively, the following two cortical polarity reversals by 1.5-2 ms. This study provides new functional data on the human MGB, and supports a more complex than simply relay-like role of the thalamus in sound perception.

Acoustic Stimulation↗

PubMed2002

Dynamics of cortico-subcortical cross-modal operations involved in audio-visual object detection in humans.

Very recently, a number of neuroimaging studies in humans have begun to investigate the question of how the brain integrates information from different sensory modalities to form unified percepts. Already, intermodal neural processing appears to depend on the modalities of inputs or the nature (speech/non-speech) of information to be combined. Yet, the variety of paradigms, stimuli and technics used make it difficult to understand the relationships between the factors operating at the perceptual level and the underlying physiological processes. In a previous experiment, we used event-related potentials to describe the spatio-temporal organization of audio-visual interactions during a bimodal object recognition task. Here we examined the network of cross-modal interactions involved in simple detection of the same objects. The objects were defined either by unimodal auditory or visual features alone, or by the combination of the two features. As expected, subjects detected bimodal stimuli more rapidly than either unimodal stimuli. Combined analysis of potentials, scalp current densities and dipole modeling revealed several interaction patterns within the first 200 micro s post-stimulus: in occipito-parietal visual areas (45-85 micro s), in deep brain structures, possibly the superior colliculus (105-140 micro s), and in right temporo-frontal regions (170-185 micro s). These interactions differed from those found during object identification in sensory-specific areas and possibly in the superior colliculus, indicating that the neural operations governing multisensory integration depend crucially on the nature of the perceptual processes involved.

Acoustic Stimulation↗