Tahamina Begum

Altered plasticity of the human motor cortex in Parkinson's disease

Interventional paired associative stimulation (IPAS) to the contralateral peripheral nerve and cerebral cortex can enhance the primary motor cortex (M1) excitability with two synchronously arriving inputs. This study investigated whether dopamine contributed to the associative long‐term potentiation–like effect in the M1 in Parkinsons disease (PD) patients. Eighteen right‐handed PD patients and 11 right‐handed age‐matched healthy volunteers were studied. All patients were studied after 12 hours off medication with levodopa replacement (PD‐off). Ten patients were also evaluated after medication (PD‐on). The IPAS comprised a single electric stimulus to the right median nerve at the wrist and subsequent transcranial magnetic stimulation of the left M1 with an interstimulus interval of 25 milliseconds (240 paired stimuli every 5 seconds for 20 minutes). The motor‐evoked potential amplitude in the right abductor pollicis brevis muscle was increased by IPAS in healthy volunteers, but not in PD patients. IPAS did not affect the motor‐evoked potential amplitude in the left abductor pollicis brevis. The ratio of the motor‐evoked potential amplitude before and after IPAS in PD‐off patients increased after dopamine replacement. Thus, dopamine might modulate cortical plasticity in the human M1, which could be related to higher order motor control, including motor learning. Ann Neurol 2006

Low-frequency rTMS over lateral premotor cortex induces lasting changes in regional activation and functional coupling of cortical motor areas

OBJECTIVE To study the effect of 0.9 Hz repetitive transcranial magnetic stimulation (rTMS) of the lateral premotor cortex on neuronal activity in cortical motor areas during simple motor tasks. METHODS In 8 subjects, electroencephalogram (EEG) and electromyogram (EMG) were simultaneously recorded during voluntary contractions of the thumb before and after a 15 min train of 0.9 Hz rTMS over the left lateral premotor cortex at stimulus intensity of 90% of active motor threshold. After-effects on cortical motor activity were assessed by measuring the task-related EEG power and inter-regional coherence changes, and the EEG-EMG coherence (EMGCoh). RESULTS Low-frequency rTMS over the premotor cortex gave rise to (i) a reduction of the task-related power decrease in the alpha and beta bands, (ii) a selective increase in the task-related coherence change among cortical motor areas in the upper alpha band, and (iii) a decrease in the cortico-muscular coherence. These effects lasted about 15 min after the end of rTMS intervention. CONCLUSIONS The attenuated task-related power changes and decreased EMGCoh point to a lasting suppression of voluntary activation of cortical motor areas after rTMS. The present data provide an evidence for a transient reorganization of movement-related neuronal activity in the cortical motor areas after 0.9 Hz rTMS over the premotor cortex. SIGNIFICANCE Low-frequency rTMS changes the regional activation and functional coupling of cortical motor areas as demonstrated by EEG analysis.

Low-frequency repetitive transcranial magnetic stimulation for seizure suppression in patients with extratemporal lobe epilepsy-—A pilot study

We evaluated the effect of low-frequency repetitive transcranial magnetic stimulation (rTMS) on seizure frequency in adult patients with medically intractable extratemporal lobe epilepsy (ETLE). Seven patients with medically intractable ETLE received low-frequency rTMS at 0.9 Hz, basically two sets of 15 min stimulation per day for five days in a week, with the stimulus intensity of 90% of resting motor threshold (RMT). The number of seizures during two weeks before and after the stimulation of one week was compared. Furthermore, RMT and active motor threshold (AMT) were measured before and after rTMS for each daily session. After low-frequency rTMS of one week, the frequency of all seizure types, complex partial seizures (CPSs) and simple partial seizures was reduced by 19.1, 35.9 and 7.4%, respectively. The patients with smaller difference between RMT and AMT before rTMS had higher reduction rate of CPSs. A favorable tendency of seizure reduction, though not statistically significant, during two weeks after low-frequency rTMS was demonstrated in medically intractable ETLE patients. As far as CPSs are concerned, smaller decrease of motor threshold by voluntary muscle contraction was associated with better response to rTMS.

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.

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.

Short-lasting impairment of tactile perception by 0.9Hz-rTMS of the sensorimotor cortex

To test whether low-frequency repetitive transcranial magnetic stimulation (rTMS) of sensorimotor cortex (SM1) has prolonged effects on somatosensory function, eight subjects were given 900 TMS pulses over the left hand SM1 (0.9Hz, 90% of the resting motor threshold) or at sites 3 cm anterior or posterior to it. Tactile threshold of the right hand was increased for a short duration after rTMS over SM1, but two-point discrimination and median nerve SEPs were unaffected after rTMS at any sites.

Brain-derived neurotrophic factor-mediated retrograde signaling required for the induction of long-term potentiation at inhibitory synapses of visual cortical pyramidal neurons

High-frequency stimulation (HFS) induces long-term potentiation (LTP) at inhibitory synapses of layer 5 pyramidal neurons in developing rat visual cortex. This LTP requires postsynaptic Ca2+ rise for induction, while the maintenance mechanism is present at the presynaptic site, suggesting presynaptic LTP expression and the necessity of retrograde signaling. We investigated whether the supposed signal is mediated by brain-derived neurotrophic factor (BDNF), which is expressed in pyramidal neurons but not inhibitory interneurons. LTP did not occur when HFS was applied in the presence of the Trk receptor tyrosine kinase inhibitor K252a in the perfusion medium. HFS produced LTP when bath application of K252a was started after HFS or when K252a was loaded into postsynaptic cells. LTP did not occur in the presence of TrkB-IgG scavenging BDNF or function-blocking anti-BDNF antibody in the medium. In cells loaded with the Ca2+ chelator BAPTA, the addition of BDNF to the medium enabled HFS to induce LTP without affecting baseline synaptic transmission. These results suggest that BDNF released from postsynaptic cells activates presynaptic TrkB, leading to LTP. Because BDNF, expressed activity dependently, regulates the maturation of cortical inhibition, inhibitory LTP may contribute to this developmental process, and hence experience-dependent functional maturation of visual cortex.

Partial Epilepsy Manifesting Atonic Seizure: Report of Two Cases

Summary:  Purpose: Atonic seizures are commonly seen in patients with generalized epilepsy but only infrequently in patients with partial epilepsy. Clinically generalized atonic seizures as a partial epilepsy have not been studied in detail with video/EEG monitoring. Here we describe the clinical and physiologic characteristics of atonic seizures due to partial epilepsy and discuss the underlying mechanism.

A survey of methods used for source localization using EEG signals

Abstract The EEG source localization which is used to localize the electrical activity of brain has been an active area of research as it provides useful information for study of brains physiological, mental and functional abnormalities. This problem is called EEG inverse problem. The localization of the active sources needs the solution of ill posed EEG inverse problem. Since the foundation of this field till today, many methods have been developed with the aim of in-depth localization, high resolution, reduction in localization/energy error and decreased computational time. In this survey, EEG inverse problem is discussed with its primary to most developed and recent solutions. The introduction to the field along with the categorization of different solutions is provided. Also, the relative advantages and limitations for each method are discussed. Finally, the challenges and future recommendations are provided, in the end, for further improvement of EEG inverse problem in terms of resolution, computational power and localization error.

Cortical mechanisms of unilateral voluntary motor inhibition in humans

While motor control is very often a goal-oriented event, little is known about the mechanisms underlying the termination of motor performance. To investigate what type of cortical activation underlies the muscle relaxation required to terminate the act, we performed single- and double-pulse transcranial magnetic stimulation (TMS) studies during voluntary muscle relaxation in nine normal volunteers. Subjects maintained a weak isometric contraction of the right first dorsal interosseous muscle (FDI), and either increased the level of contraction (Contraction), terminated the contraction (Relaxation), or maintained it (No-go) depending on a visual cue. Motor evoked potentials (MEP) and the silent period (SP) were recorded from the FDI during motor activity. To measure intra-cortical inhibition (ICI), we also performed double-pulse TMS, applying subthreshold conditioning stimuli at interstimulus intervals of 2 ms. When single-pulse TMS was given just prior to muscle relaxation (-21 to -70 ms), the MEP was reduced while the SP was unchanged. Intra-cortical inhibition was smaller just prior to the muscle relaxation. Unilateral voluntary muscle relaxation may not be associated with activation of the intracortical inhibitory system, but rather with the possible excitation of the corticospinal system, which can inhibit motoneurons disynaptically. These findings suggest that multiple inhibitory mechanisms act in diverse ways to achieve motor inhibition.