Riki Matsumoto

Primary somatosensory cortex is actively involved in pain processing in human

We recorded somatosensory evoked magnetic fields (SEFs) by a whole head magnetometer to elucidate cortical receptive areas involved in pain processing, focusing on the primary somatosensory cortex (SI), following painful CO(2) laser stimulation of the dorsum of the left hand in 12 healthy human subjects. In seven subjects, three spatially segregated cortical areas (contralateral SI and bilateral second (SII) somatosensory cortices) were simultaneously activated at around 210 ms after the stimulus, suggesting parallel processing of pain information in SI and SII. Equivalent current dipole (ECD) in SI pointed anteriorly in three subjects whereas posteriorly in the remaining four. We also recorded SEFs following electric stimulation of the left median nerve at wrist in three subjects. ECD of CO(2) laser stimulation was located medial-superior to that of electric stimulation in all three subjects. In addition, by direct recording of somatosensory evoked potentials (SEPs) from peri-Rolandic cortex by subdural electrodes in an epilepsy patient, we identified a response to the laser stimulation over the contralateral SI with the peak latency of 220 ms. Its distribution was similar to, but slightly wider than, that of P25 of electric SEPs. Taken together, it is postulated that the pain impulse is received in the crown of the postcentral gyrus in human.

Low-frequency electric cortical stimulation has an inhibitory effect on epileptic focus in mesial temporal lobe epilepsy

Summary:  Purpose: This study was conducted to investigate the effect of low‐frequency electric cortical stimulation on epileptic focus in humans.

Focal Semiologic and Electroencephalographic Features in Patients with Juvenile Myoclonic Epilepsy

Summary:  Purpose: A few reports have described focal electroencephalographic or clinical features or both of juvenile myoclonic epilepsy (JME), but without video‐EEG documentation. We examined focal clinical and EEG features in patients with JME who underwent video‐EEG monitoring.

Electrocorticogram–electromyogram coherence during isometric contraction of hand muscle in human

OBJECTIVE To clarify how the primary sensorimotor and supplementary motor areas are involved in the generation of the rhythmicity of electromyogram (EMG) activity during continuous muscle contraction. METHOD We analyzed the coherence between subdurally recorded cortical electroencephalograms (EEG) and EMGs of the contralateral wrist extensor muscle during continuous isometric contraction in 8 patients with medically intractable epilepsy. RESULTS In all subjects, a significant coherence between the primary motor area (M1) and EMG was observed at the peak frequency of 15+/-3 Hz (means+/-SD). In the primary somatosensory area (S1) of 7 subjects and the supplementary motor area proper (SMA proper) of 4 subjects, significant coherence with EMG was observed at 12+/-5 and 15+/-4 Hz, respectively. The time lags revealed by cross-correlogram were 10+/-3, 7+/-1 and 22+/-8 ms in the M1, S1 and SMA proper, respectively, with the EMG lagging in all areas. CONCLUSION These findings suggest that the rhythmic activity in the SMA proper, as well as in the S1 and M1, is related to the generation of the rhythmicity of EMG activity.

Parieto-frontal network in humans studied by cortico-cortical evoked potential

Parieto‐frontal network is essential for sensorimotor integration in various complex behaviors, and its disruption is associated with pathophysiology of apraxia and visuo‐spatial disorders. Despite advances in knowledge regarding specialized cortical areas for various sensorimotor transformations, little is known about the underlying cortico‐cortical connectivity in humans. We investigated inter‐areal connections of the lateral parieto‐frontal network in vivo by means of cortico‐cortical evoked potentials (CCEPs). Six patients with epilepsy and one with brain tumor were studied. With the use of subdural electrodes implanted for presurgical evaluation, network configuration was investigated by tracking the connections from the parietal stimulus site to the frontal site where the maximum CCEP was recorded. It was characterized by (i) a near‐to‐near and distant‐to‐distant, mirror symmetric configuration across the central sulcus, (ii) preserved dorso‐ventral organization (the inferior parietal lobule to the ventral premotor area and the superior parietal lobule to the dorsal premotor area), and (iii) projections to more than one frontal cortical sites in 56% of explored connections. These findings were also confirmed by the standardized parieto‐frontal CCEP connectivity map constructed in reference to the Jülich cytoarchitectonic atlas in the MNI standard space. The present CCEP study provided an anatomical blueprint underlying the lateral parieto‐frontal network and demonstrated a connectivity pattern similar to non‐human primates in the newly developed inferior parietal lobule in humans. Hum Brain Mapp, 2012.

Intracarotid propofol test for speech and memory dominance in man

Objective: To evaluate the usefulness of propofol as an alternative drug to amobarbital for the Wada test. Methods: The authors analyzed 67 right-handed patients out of 123 patients who were candidates for neurosurgical therapy and thus underwent the Wada test as a preoperative evaluation. Twelve were tested with propofol and 55 were tested with amobarbital. Test conditions of the Wada test, recovery time of muscle power to manual muscle testing (MMT) Grade 3 (T3/5) and Grade 5 (T5/5), onset time of the first verbal response (Tverb) after injection and that of the first nonverbal response (Tnon-verb), were compared between the two groups. Power spectrum analysis of EEG background activity during the Wada test was performed and the time and spatial distribution of polymorphic slow activities were also compared in three cases. Results: With propofol injection, lateralities of language and memory function were identified in 12 and 9 of 12 patients in comparison to amobarbital (52 and 41 of 55 patients detection in language and memory function). No complications with direct intracarotid injection of propofol were observed. T3/5 and T5/5 with propofol injection were shorter while Tverb and Tnon-verb were longer compared to amobarbital. Absolute power of polymorphic slow EEG waves gradually increased and then rapidly decreased with propofol, which was in contrast to amobarbital injection. Conclusions: With direct intracarotid propofol injection, the Wada test was satisfactorily performed in all 12 patients and 2 more patients with left-handedness or with different injection dose for each side without any complications. Clinical usefulness of propofol as an alternative drug to amobarbital for the Wada test was indicated.

Electric Stimulation on Human Cortex Suppresses Fast Cortical Activity and Epileptic Spikes

Summary:  Purpose: To investigate underlying mechanisms and adequate parameters for electric cortical stimulation to inhibit epileptic focus in humans.

Direct Exploration of the Role of the Ventral Anterior Temporal Lobe in Semantic Memory: Cortical Stimulation and Local Field Potential Evidence From Subdural Grid Electrodes

Semantic memory is a crucial higher cortical function that codes the meaning of objects and words, and when impaired after neurological damage, patients are left with significant disability. Investigations of semantic dementia have implicated the anterior temporal lobe (ATL) region, in general, as crucial for multimodal semantic memory. The potentially crucial role of the ventral ATL subregion has been emphasized by recent functional neuroimaging studies, but the necessity of this precise area has not been selectively tested. The implantation of subdural electrode grids over this subregion, for the presurgical assessment of patients with partial epilepsy or brain tumor, offers the dual yet rare opportunities to record cortical local field potentials while participants complete semantic tasks and to stimulate the functionally identified regions in the same participants to evaluate the necessity of these areas in semantic processing. Across 6 patients, and utilizing a variety of semantic assessments, we evaluated and confirmed that the anterior fusiform/inferior temporal gyrus is crucial in multimodal, receptive, and expressive, semantic processing.

Multisensory convergence at human temporo-parietal junction – epicortical recording of evoked responses

OBJECTIVE Previous lesion studies in patients and functional imaging studies in normal subjects have led to the notion that the temporo-parietal junction (TPJ) has an integrative function for multisensory inputs. However, its electrophysiological properties such as response latencies and distributions of responses to various stimulus modalities in humans have not been fully investigated. The aim of the study is to clarify this issue. METHODS We recorded evoked potentials to different kinds of sensory stimuli including somatosensory, auditory and visual modalities in 6 patients with intractable partial epilepsy, who underwent chronic implantation of subdural electrodes in TPJ for presurgical evaluation. RESULTS In 5 out of 6 subjects, at least one electrode located in TPJ for each subject showed a maximum somatosensory evoked response commonly to electric, passive joint motion and pain stimuli. These electrodes showed the maximum responses also to tone stimuli in all of 4 subjects studied, and to visual motion stimuli in 3 out of 5 subjects studied. The polarity was consistent regardless of the stimulus modality within each individual subject, although the anatomical location, polarity and latency varied among subjects. CONCLUSIONS A small area in TPJ for each individual subject receives sensory information of multiple modalities possibly coming from different receptive sites, although the electrophysiological properties of the responses may vary among subjects. SIGNIFICANCE We confirmed the convergence of somatosensory, auditory and visual evoked responses at human TPJ.

Hemispheric asymmetry of the arcuate fasciculus : A preliminary diffusion tensor tractography study in patients with unilateral language dominance defined by Wada test

ObjectiveLateralization of language function is a prominent feature of human brain function, and its underlying structural asymmetry has been recently reported in normal right-handed subjects. By means of diffusion tensor tractography (DTT), we investigated the asymmetry of the language network, namely, the arcuate fasciculus in patients in whom the unilateral language dominance was defined by Wada test.MethodsDTT was performed in 24 patients with a focal lesion or an epileptic focus outside the C-shaped segment of the arcuate fasciculus. The arcuate fasciculus was reconstructed by placing two regions-of-interest in the deep white matter lateral to the corona radiata. The pathway was then divided into one terminating in the temporal lobe (FT tract) and the other in the parietal lobe (FP tract). The relative number and volume of the FT and FP tracts in each hemisphere were submitted to repeated measure ANOVA separately, with the hemisphere as a within-subject factor and with the side of pathology as a betweensubject factor.ResultsThe FT tract showed a significantly larger number and volume in the language dominant hemisphere than in the non-dominant hemisphere, while, for the FP tract, no significant hemispheric difference was observed in the relative number or volume. There was a tendency that the FT tract was less lateralized when the pathology was located in the dominant hemisphere than in the non-dominant hemisphere.ConclusionDominance of the FT tract in the language dominant hemisphere was demonstrated for the first time in a patient population and implicated a clinical utility of DTT for non-invasive evaluation of language lateralization. Our preliminary study might indicate reorganization of the language network in conjunction with pathology.