Antoine Ducorps

Human brain mapping in dystonia reveals both endophenotypic traits and adaptive reorganization

Dystonia has a wide clinical spectrum from early‐onset generalized to late‐onset sporadic, task‐specific forms. The genetic origin of the former has been clearly established. A critical role of repetitive skilled motor tasks has been put forward for the latter, while underlying vulnerability traits are still being searched for. Using magnetoencephalography, we looked for structural abnormalities reflecting a preexisting dysfunction. We studied finger representations of both hands in the primary sensory cortex, as compared in 23 patients with unilateral task‐specific dystonia and 20 control subjects. A dramatic disorganization of the nondystonic hand representation was found in all patients, and its amount paralleled the severity of the dystonic limb motor impairment. Abnormalities were also observed in the cortex coding the dystonic limb representation, but they were important only in the most severely affected patients. The abnormal cortical finger representations from the nondystonic limb appear to be endophenotypic traits of dystonia. That finger representations from the dystonic limb were almost normal for the less severely affected patients may be due to intrinsic beneficial remapping in reaction against the primary disorder.

Simultaneous MEG and intracranial EEG recordings during attentive reading

The relationship between neural oscillations recorded at various spatial scales remains poorly understood partly due to an overall dearth of studies utilizing simultaneous measurements. In an effort to study quantitative markers of attention during reading, we performed simultaneous magnetoencephalography (MEG) and intracranial electroencephalography (iEEG) recordings in four epileptic patients. Patients were asked to attend to a specific color when presented with an intermixed series of red words and green words, with words of a given color forming a cohesive story. We analyzed alpha, beta, and gamma band oscillatory responses to the word presentation and compared the strength and spatial organization of those responses in both electrophysiological recordings. Time-frequency analysis of iEEG revealed a network of clear attention-modulated high gamma band (50-150 Hz) power increases and alpha/beta (9-25 Hz) suppressions in response to the words. In addition to analyses at the sensor level, MEG time-frequency analysis was performed at the source level using a sliding window beamformer technique. Strong alpha/beta suppressions were observed in MEG reconstructions, in tandem with iEEG effects. While the MEG counterpart of high gamma band enhancement was difficult to interpret at the sensor level in two patients, MEG time-frequency source reconstruction revealed additional activation patterns in accordance with iEEG results. Importantly, iEEG allowed us to confirm that several sources of gamma band modulation observed with MEG were indeed of cortical origin rather than EMG muscular or ocular artifact.

Simultaneous MEG-intracranial EEG: New insights into the ability of MEG to capture oscillatory modulations in the neocortex and the hippocampus

Epilepsy is, of course, not one disease but rather a huge number of disorders that can present with seizures. In common, they all reflect brain dysfunction. Moreover, they can affect the mind and, of course, behavior. While animals too may suffer from epilepsy, as far as we know, the electrical discharges are less likely to affect the mind and behavior, which is not surprising. While the epileptic seizures themselves are episodic, the mental and behavioral changes continue, in many cases, interictally. The episodic mental and behavioral manifestations are more dramatic, while the interictal ones are easier to study with anatomical and functional studies. The following extended summaries complement those presented in Part 1.

Tonotopic cortical representation of periodic complex sounds

Most of the sounds that are biologically relevant are complex periodic sounds, i.e., they are made up of harmonics, whose frequencies are integer multiples of a fundamental frequency (Fo). The Fo of a complex sound can be varied by modifying its periodicity frequency; these variations are perceived as the pitch of the voice or as the note of a musical instrument. The center frequency (CF) of peaks occurring in the audio spectrum also carries information, which is essential, for instance, in vowel recognition. The aim of the present study was to establish whether the generators underlying the 100m are tonotopically organized based on the Fo or CF of complex sounds. Auditory evoked neuromagnetic fields were recorded with a whole‐head magnetoencephalography (MEG) system while 14 subjects listened to 9 different sounds (3 Fo × 3 CF) presented in random order. Equivalent current dipole (ECD) sources for the 100m component show an orderly progression along the y‐axis for both hemispheres, with higher CFs represented more medially. In the right hemisphere, sources for higher CFs were more posterior, while in the left hemisphere they were more inferior. ECD orientation also varied as a function of the sound CF. These results show that the spectral content CF of the complex sounds employed here predominates, at the latency of the 100m component, over a concurrent mapping of their periodic frequency Fo. The effect was observed both on dipole placement and dipole orientation. Hum. Brain Mapping 20:71–81, 2003.

A cortical map for tempo

Tonotopy is a well‐known property of the brain which consists of a linearly organized representation of the tonal frequencies on the auditory cortex. A similar organization for the rate of auditory events (tempo) is demonstrated. Subjects listened to isochronous, isotonic sequences of pure tones varying in tempo (100‐, 200‐, 250‐, 300‐, 400‐, 800‐, and 1600‐ms IOI) and frequency (400, 1000, and 2500 Hz). Brain magnetic activity (MEG) was recorded over the whole skull with a 150‐sensor array. For slow tempi (above 300‐ms IOI), sources of brain magnetic activity occurring 100 ms after stimulus onset (M100) were localized in the auditory cortex of both hemispheres. Source position varied systematically as a function of tempo and frequency: (1) on a transverse line for different tempi, more laterally in both hemispheres for the slower tempi (‘‘tempotopy’’), and (2) on an anteroposterior line for different frequencies, more anterior for the higher frequencies (tonotopy). For fast tempi, the main observed MEG r...