Biomedical subjects

R Hanajima

Publications and source records attributed to R Hanajima.

42 records · Page 3Linked to original sources

PubMed1995

Altered motor cortical excitability to magnetic stimulation in a patient with a lesion in globus pallidus.

A 27-year-old man with Behçet's disease presented with dyskinesia of the right hand and leg, but without paresis. MRI showed a discrete lesion in the internal segment of the left globus pallidus. SPECT (single photon emission tomography) disclosed increased perfusion in the hand and leg area of the left motor cortex and ipsilateral thalamus compared to that of the corresponding regions on the right. The dyskinesia was considered to be produced by disinhibition of the motor cortex due to loss of inhibitory inputs from the ipsilateral pallidum via the thalamus. Double transcranial magnetic stimulation revealed loss of suppression (loss of intracortical inhibition) of the left motor cortex while it showed normal suppression on the right, even though conventional techniques of magnetic stimulation failed to show any changes in excitability of the left motor cortex. We conclude that it is possible to detect changes of motor cortical excitability caused by dysfunction of some inputs from the basal ganglia by using the double cortical stimulation technique here described.

Adult↗

PubMed1995

Input-output organization in the hand area of the human motor cortex.

The primate motor cortex consists of efferent zones which receive sensory information from a portion of limb in close anatomical relation to the muscle to which they project. To investigate a similar input-output relation in humans, we studied the effect of tactile stimuli on the size of motor evoked potentials (MEPs) elicited by transcranial magnetic and electrical stimulation. For tactile stimuli we applied air to the skin. The sizes of MEP of 3 finger muscles (flexor pollicis brevis, first dorsal interosseous, and abductor digiti minimi) with and without air stimuli were compared. Air stimuli applied to the tip of one finger facilitated mainly the magnetically evoked MEP of a muscle attached to that finger. A less obvious facilitatory effect was observed when giving stimuli on the dorsal aspect of the hand. Air stimuli had no facilitatory effect on electrically evoked MEPs. In one subject, there was no facilitatory effect even to magnetically evoked MEPs. In this subject, D-waves had the lowest threshold for magnetic and electrical stimulation. These results suggested that the effect was produced at the cortical level. This effect may correspond to the input-output relation found in the primate motor cortex.

Electric Stimulation↗

PubMed1995

Facilitatory effect of tonic voluntary contraction on responses to motor cortex stimulation.

To investigate the mechanisms underlying the facilitation of responses to motor cortical stimulation produced by tonic voluntary contraction, we studied the facilitatory effects in 7 normal volunteers during different levels of muscle contraction. Responses were similarly facilitated by voluntary contraction with 3 forms of stimulation: magnetic cortical, electrical cortical, and foramen magnum level stimulation. At a high level of contraction, however, only magnetic responses were markedly facilitated. We conclude that the facilitation of responses to cortical stimulation induced by tonic voluntary contraction occurs mainly at the spinal level, but that cortical excitability changes also contribute to the enlargement of magnetic responses in the case of a high level of contraction.

Adult↗

PubMed1994

Magnetic stimulation of corticospinal pathways at the foramen magnum level in humans.

Magnetic stimulation done with a double cone coil placed over the back of the head activated descending motor pathways and produced electromyographic responses in muscles of the arms and legs. The latencies of these responses were the same as those of responses to electrical brainstem stimulation. The threshold was lowest when the coil was placed over the inion or below it on the median line. Placement of the coil on the side ipsilateral to the muscle was more effective than placement on the contralateral side. These results indicate that activation occurs at the foramen magnum level (just below the pyramidal decussation). Collision experiments that used cortical and magnetic brainstem stimulation indicated that the major part of the responses to the latter stimulation were conducted via the large diameter component of the corticospinal tract. Collision experiments done with the peripheral nerve and magnetic brainstem stimulation showed that this stimulation produced a single descending volley in the descending tract. We conclude that magnetic brainstem stimulation produces a single descending volley in the corticospinal tract at the foramen magnum level with less discomfort.

Adult↗

PubMed1994

Motor cortex inhibition in patients with ataxia.

We studied the effects of a subthreshold magnetic stimulus over the motor cortex and an electrical stimulus over the cerebellum on EMG responses produced by a suprathreshold magnetic stimulus over the motor cortex. In normal subjects, both subthreshold conditioning stimuli and cerebellar stimuli could suppress responses to suprathreshold magnetic test stimuli when given at appropriate timings: "cortico-cortical" and "cerebellar" inhibition, respectively. In all patients with degenerative ataxias and patients with a lesion in the cerebellar thalamus, the "cortico-cortical" inhibition was normal and the "cerebellar" inhibition was absent. We conclude that cerebellar systems make no or little contribution to the above-mentioned "cortico-cortical" inhibition.

Adult↗

PubMed1993

Interhemispheric facilitation of the hand area of the human motor cortex.

We investigated interaction of the human bilateral hand motor area using two magnetic stimulators. A conditioning shock over the motor cortex facilitated the response evoked in the ipsilateral first dorsal interosseous muscle by a test shock over the contralateral motor cortex given under the limiting conditions of a small conditioning shock over a very small area and a small test shock. This effect was so weak that it was not elicited under slightly different conditions. We conclude that an excitatory, but weak, connection between strictly homotopic areas of the bilateral hand motor cortices exists in humans.

Adult↗