Intracortical modulation of somatosensory evoked fields during movement: evidence for selective suppression of postsynaptic inhibition.

As accurate finger movements depend on guidance by afferent sensory feedback information, it is of interest to examine how the cortical processing of afferent signals is altered during movement states compared with rest. In the present study we evaluated afferent input to the primary somatosensory cortex (SI) in human subjects performing a finger opposition task. We recorded somatosensory evoked magnetic fields (SEFs) in 6 healthy subjects to stimulation of left and right median nerves in a resting condition and during active right-sided finger movements.

In search of augmentation at human SI: Somatosensory cortical responses to stimulus trains and their modulation by motor activity.

In many animal preparations, repeated stimulation at ca. 10 Hz in thalamic nuclei leads to rapid changes in the cortical evoked responses, known as the augmenting response. The present study was undertaken to evaluate whether anything similar to the augmenting response can be observed in awake human subjects when a peripheral nerve is stimulated, and whether a possible human correlate of augmenting would be modified when the subject is engaged in an active motor task.

Modulation of somatosensory evoked fields from SI and SII by acute GABA A-agonism and paired-pulse stimulation.

The purpose of the present study was to shed light on the physiology underlying somatosensory evoked magnetic fields (SEFs) by means of pharmacological manipulation with the GABA A agonist lorazepam and paired-pulse stimulation. SEFs were recorded from the primary (SI) and secondary (SII) somatosensory cortices following median nerve stimulation. Responses were obtained to single stimuli every 2 s and to paired stimuli with interpulse intervals (IPIs) of 20 ms and 100 ms.

Sensorimotor cortex localization: comparison of magnetoencephalography, functional MR imaging, and intraoperative cortical mapping.

Purpose: To prospectively evaluate magnetoencephalography (MEG) and functional magnetic resonance (MR) imaging, as compared with intraoperative cortical mapping, for identification of the central sulcus.

Materials And Methods: Fifteen patients (six men, nine women; age range, 25-58 years) with a lesion near the primary sensorimotor cortex (13 gliomas, one cavernous hemangioma, and one meningioma) were examined after institutional review board approval and written informed consent from each patient were obtained. At MEG, evoked magnetic fields to median nerve stimulation were recorded; at functional MR imaging, hemodynamic responses to self-paced palmar flexion of the wrist were imaged.

Spatial dynamics of population activities at S1 after median and ulnar nerve stimulation revisited: an MEG study.

In a number of studies, magnetoencephalography (MEG) has been successfully employed in localizing cortical neural population activities after stimulation of peripheral nerves. Little attention has been paid, however, to the spatiotemporal dynamics of these activations within the primary somatosensory cortex (SI). Here we report on the activation sequence at the right SI after left median and ulnar nerve stimulation.

Effects of an acute D2-dopaminergic blockade on the somatosensory cortical responses in healthy humans: evidence from evoked magnetic fields.

We tested the possible role of dopaminergic activity in the processing of somatosensory afferent information in healthy humans. Somatosensory evoked magnetic fields (SEFs) were recorded in seven subjects in response to left median nerve stimulation. SEFs were obtained in all subjects after oral administration of 2 mg haloperidol, an antagonist to dopaminergic D2 receptors, and placebo, which were given in a randomized, double-blind cross-over design.

Effects of scopolamine on MEG spectral power and coherence in elderly subjects.

Objective: Scopolamine, a muscarinic receptor antagonist, can produce temporary cognitive impairments as well as electroencephalographic changes that partially resemble those observed in Alzheimer's disease. In order to test the sensitivity of spectral power and hemispheric coherence to changes in cholinergic transmission, we evaluated quantitative magnetoencephalogram (MEG) after intravenous injection of scopolamine.

Methods: MEG of 8 elderly healthy subjects (59-80 years) were measured with a whole-head magnetometer after intravenous injection of scopolamine.

Dopamine modulates involuntary attention shifting and reorienting: an electromagnetic study.

Objective: Dopaminergic function has been closely associated with attentional performance, but its precise role has remained elusive.

Methods: Electrophysiological and behavioral methods were used to assess the effects of dopamine D2-receptor antagonist haloperidol on involuntary attention shifting using a randomized, double-blind, placebo-controlled cross-over design. Eleven subjects were instructed to discriminate equiprobable 200 and 400ms tones in a forced-choice reaction-time (RT) task during simultaneous measurement of whole-head magnetoencephalography and high-resolution electroencephalography.

Memory-based comparison process not attenuated by haloperidol: a combined MEG and EEG study.

Auditory P50 and N100 responses reflect preattentive processing, whereas subsequent mismatch negativity (MMN) response indexes memory-based comparison process. Divergent ERP responses have been found in schizophrenia and in Parkinson's disease (PD), which have abnormalities in cerebral dopamine activity. We used simultaneously magnetoencephalography and electroencephalography to investigate, whether a single dose of haloperidol, a dopamine D2-receptor antagonist, modulates preattentive auditory processing using a randomized, double-blind, placebo-controlled crossover design.

Ipsi- and contralateral EEG reactions to transcranial magnetic stimulation.

Objectives: Transcranial magnetic stimulation (TMS) and high-resolution electroencephalography (EEG) were used to study the spreading of cortical activation in 6 healthy volunteers.

Methods: Five locations in the left sensorimotor cortex (within 3cm(2)) were stimulated magnetically, while EEG was recorded with 60 scalp electrodes. A frameless stereotactic method was applied to determine the anatomic locus of stimulation and to superimpose the results on magnetic resonance images.