Transcallosal Conduction Time Research Articles

A transcranial magnetic stimulation study of the ipsilateral silent period in lower limb muscles

The lower limb ipsilateral silent periods (ISP) were determined with transcranial magnetic stimulation in 30 normal subjects using a round coil. The mean duration and transcallosal conduction time were comparable to values obtained from upper limb recordings. No age-related correlation was found for either parameter, corroborating previous imaging and pathological studies of interhemispheric pathways. Our results highlight the feasibilty of eliciting ISPs in the lower limbs, relevant for future studies of interhemispheric interaction in clinical and research settings.

Dissociation, Hemispheric Asymmetry, and Dysfunction of Hemispheric Interaction: A Transcranial Magnetic Stimulation Approach

The authors investigated the hypothesis that dissociation may represent a functional dysconnectivity syndrome using a transcranial magnetic stimulation (TMS) approach. Transcranial magnetic stimulation investigations that included motor thresholds and the transcallosal conduction time (TCT) reflecting the interhemispheric transfer were performed in 74 right-handed students. All subjects completed the Dissociative Experience Scale. The high dissociators had a significantly lower left hemispheric excitability than right hemispheric excitability. They also had a significantly shorter TCT from the left to the right hemisphere than did the low dissociators. These results suggest that the neural basis of dissociation may involve a cortical asymmetry with a left hemispheric superiority or, alternatively, a lack of right hemispheric integration.

Interhemispheric Transfer in Alexithymia: A Transcallosal Inhibition Study

Objective: This study investigates the hypothesis that alexithymia is associated with an interhemispheric transfer deficit via the corpus callosum (CC). Method: The transcallosal inhibition paradigm was used to assess interhemispheric transfer. Transcranial magnetic stimulation (TMS) and peripheral electromyographic recordings were performed in 10 right-handed male and 10 female students with Toronto Alexithymia Scale (TAS-20) scores of ≧61 and controls (TAS-20 scores of <61). The transcallosal conduction time (TCT) reflects the TMS-induced inhibitory cortical activity that is mediated via the CC. Results: There was a significant interaction between gender and alexithymia (Wilks λ = 0.89; F = 3.4; d.f. = 2, 57; p = 0.04) indicating that alexithymic males had shorter bidirectional TCTs than controls and a significantly shorter left to right TCT than controls (p = 0.002). However, the left to right TCT was not significantly different from the right to left TCT in alexithymic males (p = 0.39). Alexithymic females were not different from controls. Conclusion: Our results clearly stand in contrast to the hypothesis of a transfer deficit due to a dysfunction of the CC in alexithymia. Facilitated, bidirectional transcallosal inhibition of the contralateral motor activity is associated with alexithymia in males. Facilitated cortical inhibition may be a neurobiological correlate of alexithymia.

Transcallosal conduction time measured by visual hemifield stimulation with face images.

Transcallosal conduction time (TCT) in human visual system was estimated from the hemispheric difference of the peak latencies of face-evoked magnetic field (N170m) by left/right hemifield stimulation using 14 8 channel whole-head magnetometers. The estimated TCTwas 18.0 + 6.2 ms (mean +/- s.d.). Although N 170m amplitude was larger in the right hemisphere of seven of nine subjects, no hemispheric asymmetry was observed in the TCT estimate. Transcallosal visual information was likely to be transferred in the higher order (non-retinotopic) visual cortices. Hemifield stimulation with face images is a useful non-invasive method to estimate the TCT in human visual system.

Visual transcallosal conduction time measured by hemifield stimulation with face images

Visual transcallosal conduction time measured by hemifield stimulation with face images

Transcallosal inhibition and motor conduction studies in patients with schizophrenia using transcranial magnetic stimulation.

Transcranial magnetic stimulation of the motor cortex may not only elicit excitatory responses in hand muscles contralateral to the stimulated hemisphere, but may also suppress tonic voluntary electromyogram activity in muscles ipsilateral to the stimulation. This inhibition is mediated between the motor cortices via the corpus callosum. To investigate motor excitability and interhemispheric (transcallosal) connections in patients with schizophrenia. Transcallosal inhibition and motor conduction parameters were investigated in ten patients with schizophrenia and in ten age- and gender-matched healthy subjects. Transcallosal conduction time (TCT) and duration of the inhibition were significantly longer in patients with schizophrenia (mean (s.d.)): TCT, 12.4 (2.9) ms in normal subjects and 15.3 (2.6) ms in patients (P = 0.03); mean duration, 34.1 (4.9) ms in normal subjects and 51.9 (16.8) ms in patients (P = 0.01). Magnetic motor conduction parameters are unaltered in schizophrenia, but transcallosal inhibition is significantly delayed and prolonged. This may indicate abnormal function of the corpus callosum in these patients.

Altersabhängigkeit der inter-hemisphärischen Inhibition des Motorkortex beim Menschen

Ongoing voluntary electromyographic activity of the small hand muscles can be suppressed by a single focal magnetic stimulus applied to the ipsilateral motor cortex. This inhibition is mediated from one motor cortex to the contralateral side via a transcallosal pathway. We investigated the transcallosal inhibition in 24 healthy volunteers aged 26-80 years. The aim of this study was to investigate a possible correlation between the age and the gender of the subjects and the parameters of the transcallosal inhibition. A focal magnetic stimulus was applied to the hand area of the motor cortex and the onset latency of the inhibition of the ongoing EMG activity of the ipsilateral first dorsal interosseus muscle was evaluated. Corticomuscular conduction time to the same muscle was measured using a magnetic stimulus over the contralateral motor cortex. The difference between these values was calculated as transcallosal conduction time. All subjects had a transient complete inhibition of the EMG activity of their ipsilateral first dorsal interosseus muscle. The transcallosal conduction time was 12.2 ± 2.6 ms and the duration of the inhibition was 38.9 ± 10.1 ms. No statistically significant correlation between the age of the subjects and the transcallosal conduction time or the depth of the inhibition could be found. There was no significant difference between the transcallosal inhibition of the hemispheres or between both genders.

Interhemispheric inhibition in patients with multiple sclerosis

Objectives: A single focal magnetic stimulus applied to the motor cortex of normal subjects can suppress ongoing voluntary electromyographic activity in ipsilateral small hand muscles. This inhibition is mediated from one motor cortex to the contralateral side via a transcallosal pathway. Methods: We have investigated transcallosal inhibition in 24 patients with definite multiple sclerosis (MS) and in 24 healthy volunteers. A focal magnetic stimulus was applied to the hand area of the motor cortex and the onset latency of the inhibition of the ongoing EMG activity of the ipsilateral first dorsal interosseus muscle was evaluated. Cortico-motor conduction time to the same muscle was revealed, using a magnetic stimulus over the contralateral motor cortex. The difference between these values was calculated as transcallosal conduction time. Cerebral magnetic resonance imaging (MRI) scans including sagittal T2-weighted images were performed in 18 patients. Results: The depth of inhibition (maximal inhibition as percentage of the baseline EMG) in the MS patients was comparable to normal values, but the transcallosal conduction time was significantly delayed (patients 17.2±6.4 ms; normal subjects 12.2±2.6 ms; P<0.001). The duration of the inhibition was significantly prolonged in MS patients (patients 47.9±20.9 ms; normal subjects 38.9±10.1 ms; P=0.02). Transcallosal conduction time was delayed in 11 (46%) of 24 patients, compared with normal subjects. It exceeded the normal range (mean±2.5 SD) in one normal subject (specifity 96%). No correlation could be found between the size or extent of the lesions obtained from the MRI scan and the onset latency or the depth of the inhibition. Conclusions: We conclude that conduction over transcallosal connections is significantly slower in patients with MS.

Topography of fibers in the human corpus callosum mediating interhemispheric inhibition between the motor cortices

In 1 split-brain patient and 13 patients with circumscript surgical lesions within different parts of the corpus callosum (CC), the topography of fibers within the CC mediating an interhemispheric inhibition between the motor cortices was investigated in the phase of a stable disconnection syndrome. The aim of the study was to characterize the system of callosal fibers activated by transcranial magnetic brain stimulation in more detail as a basis for a diagnostic application of this technique. The locations and areas of the lesions were measured on sagittal magnetic resonance (MR) slices and attributed to five segments of the CC, because the borders of the anatomic subdivisions of the CC are not clearly defined. Transcallosal inhibition (TI) of tonic electromyographical hand muscle activity was elicited by focal transcranial magnetic stimulation over the primary motor cortex. In a reference group of normal subjects, TI started after 35.8+/-3.6 msec had a duration of 24.8+/-2.7 msec and an estimated transcallosal conduction time of 15.5+/-3.0 msec (range, 10.2-20.0 msec, n = 24 hands). No significant differences were found for the TI originating from the right and left motor cortices. From the absence and presence of TI in patients with lesions in different parts of the CC it can be concluded that most of the fibers mediating TI pass through the posterior third and anterior fourth segment of the CC, that is, through the posterior half of the trunk of the CC. The clinical findings suggest a role for TI in the performance of fast and complex hand motor tasks.

Inhibitory and excitatory interhemispheric transfers between motor cortical areas in normal humans and patients with abnormalities of the corpus callosum.

Transcranial magnetic stimulation of the motor cortex was performed in 10 normal subjects and 10 patients with radiographical abnormalities of the corpus callosum. Seven patients had a complete or partial agenesis or hypoplasia of the corpus callosum, two had a thin corpus callosum due to hydrocephalus or white matter degeneration and one had a circumscript contusion lesion of the corpus callosum. The patients served as a clinical model to investigate transcallosal influences on excitatory and inhibitory effects of motor cortex stimulation and to assess the potential diagnostic use of interhemispheric conduction studies and the contribution of interhemispheric interaction on transcranially elicited contralateral excitatory and inhibitory motor responses. Stimulation over one motor cortex suppressed tonic voluntary electromyographic activity in ipsilateral hand muscles in all subjects with preserved anterior half of the trunk of the corpus callosum. Since this suppression was lacking or had a delayed onset latency in patients with absence or abnormalities of the anterior half of the trunk of the corpus callosum it can be concluded that it is due to a transcallosal inhibition (Ti) of the opposite motor cortex mediated by fibres passing through this part of the corpus callosum. In normal subjects Ti had an mean onset latency of 36.1 +/- 3.5 ms (SD) and a duration of 24.5 +/- 3.9 ms. The calculated mean transcallosal conduction time was 13 ms. The threshold of Ti recorded in muscles ipsilateral to stimulation tended to be higher than the one for eliciting excitatory contralateral motor responses (56 +/- 6% versus 46 +/- 10% maximum stimulator output). Cortical thresholds (at rest) for contralateral excitatory hand motor responses were higher in patients with developmental abnormalities of the corpus callosum than in normals (66 +/- 17% versus 46 +/- 10% maximum stimulator output), which probably reflects also a facilitatory transcallosal interaction of both motor cortices in normals. In contrast, facilitation of cortically elicited motor responses in one hand by strong contraction of the other hand was the same in the patients with agenesis of the corpus callosum and normals, which suggests that this facilitatory spread takes place on a spinal rather than on a cortical level. Central motor latencies and amplitudes of contralateral hand motor responses were the same in patients with developmental abnormalities of the corpus callosum and normals (6.1 +/- 0.7 ms versus 6.3 +/- 0.7 ms and 6.7 +/- 2.4 mV versus 6.6 +/- 2.9 mV) so that callosal transfers do not seem to influence corticospinal conduction properties.(ABSTRACT TRUNCATED AT 400 WORDS)