Intracortical inhibition is reduced in a patient with a lesion in the posterolateral thalamus

Effects of spinal cord stimulation on cortical excitability in patients with chronic neuropathic pain: A pilot study

BACKGROUND

Despite a broad clinical use, the mechanism of action of SCS is poorly understood. Current information suggests that the effects of SCS are mediated by a complex set of interactions at several levels of the nervous system including spinal and supraspinal mechanisms.

AIMS

The study was undertaken to investigate the influence of SCS on distinct parameters of cortical excitability using single- and paired-pulse transcranial magnetic stimulation (TMS).

METHODS

Five patients with chronic neuropathic pain were examined with the SCS stimulator on and off by means of TMS. Pain was assessed using a visual-analogue scale. Electrophysiological and pain parameters of patients during this procedure were compared by means of a linear mixed effect model.

RESULTS

SCS induced a significant modulation of cortical excitability, especially by influencing the parameter "intracortical facilitation" (t=-2.657; df=8; p=0.029). A significant relationship between this parameter and "perceived pain" could be obtained (t=-4.798; df=8; p=0.002).

CONCLUSIONS

These results suggest that SCS is able to influence neurobiological processes at the supraspinal level and that clinical effects of SCS may be at least in part of cortical origin.

Momentary reward induce changes in excitability of primary motor cortex

OBJECTIVE

To investigate the human primary motor cortex (M1) excitability changes induced by momentary reward.

METHODS

To test the changes in excitatory and inhibitory functions of M1, motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and short-latency afferent inhibition (SAI) were tested in the abductor pollicis brevis (APB) muscle of non-dominant hand in 14 healthy volunteers by transcranial magnetic stimulation (TMS) during a behavioral task in which subjects were pseudorandomly received either reward target or non-target stimuli in response to a cue. To control sensorimotor and attention effects, a sensorimotor control task was done replacing the reward target with non-reward target.

RESULTS

The SICI was increased, and the SAI was decreased significantly during the presentation of the reward target stimuli. Those changes were not evident during non-reward target stimuli in the sensorimotor control task, indicating that this change is specific to momentary reward.

CONCLUSIONS

Momentary rewarding is associated with change in intracortical inhibitory circuits of M1.

SIGNIFICANCE

TMS may be a useful probe to study the reward system in health and in many diseases in which its dysfunction is suspected.

Functional involvement of the cerebral cortex following paramedian bithalamic infarction

To investigate further the functional mechanisms underlying the so-called 'loss of psychic self-activation' following paramedian bithalamic lesions, we used transcranial magnetic stimulation (TMS) in a patient who presented with this clinical picture after paramedian bithalamic infarction due to arterial occlusion. The patient showed higher motor thresholds than the controls; the cortical silent period and intracortical inhibition to paired-pulse stimulation, two different forms of inhibition that are believed to reflect GABAergic mechanisms, were significantly increased; short latency afferent inhibition (SAI), a technique that may give direct information about the function of some cholinergic circuits in the human brain, was significantly reduced. This study first demonstrates that there are changes in the intracortical excitatory and inhibitory circuits in this neurobehavioral syndrome, that lead to cortical hypoexcitability. The modulation in GABAergic activity may result in excitability changes in those cholinergic cortical networks that are involved in SAI. TMS may provide important information on connections between the thalamus and cortex and may help in better understanding the role of the thalamo-cortical relationship in behavioural changes associated with thalamic stroke.

Modulation of human motor cortex excitability by quetiapine

RATIONALE

Quetiapine is increasingly used for the treatment of patients with psychosis and bipolar disorder. However, the neurobiological mechanisms, which may account for the favourable risk/benefit profile of this drug, are not entirely understood.

OBJECTIVES

Transcranial magnetic stimulation was used to investigate the effects of acute and repeated administration of quetiapine on cortical excitability in healthy volunteers.

MATERIALS AND METHODS

Within a double-blind, placebo-controlled, randomized cross-over design motor threshold, intracortical inhibition, intracortical facilitation and cortical silent period were studied in 15 healthy volunteers before and after a single dose of placebo and 100 mg quetiapine. Additional measurements were performed after 5 days of daily intake of 100 mg quetiapine.

RESULTS

We observed a significant prolongation of the cortical silent period after a single dose of quetiapine, whereas the placebo had no effects. After repeated administration, there was a trend towards CSP prolongation, which did not reach significance. However, plasma concentrations at this time point were relatively low, as measurements were performed 15 h after the last drug intake. Other parameters of cortical excitability remained unaffected.

CONCLUSIONS

By lengthening CSP without affecting MT, ICI and ICF, quetiapine demonstrates a unique neurophysiological profile which differs distinctively from brain excitability profiles of typical antipsychotics such as haloperidol. Provided that the CSP prolongation reflects the antipsychotic potential of quetiapine, TMS may be developed as a tool to monitor neurobiological effects of quetiapine treatment in schizophrenic patients and to explore the efficacy of other antipsychotic drugs with a similar mode of action.

Transcranial magnetic stimulation for the treatment of tinnitus: effects on cortical excitability

Background

Low frequency repetitive transcranial magnetic stimulation (rTMS) has been proposed as an innovative treatment for chronic tinnitus. The aim of the present study was to elucidate the underlying mechanism and to evaluate the relationship between clinical outcome and changes in cortical excitability. We investigated ten patients with chronic tinnitus who participated in a sham-controlled crossover treatment trial. Magnetic-resonance-imaging and positron-emission-tomography guided 1 Hz rTMS were performed over the auditory cortex on 5 consecutive days. Active and sham treatments were separated by one week. Parameters of cortical excitability (motor thresholds, intracortical inhibition, intracortical facilitation, cortical silent period) were measured serially before and after rTMS treatment by using single- and paired-pulse transcranial magnetic stimulation. Clinical improvement was assessed with a standardized tinnitus-questionnaire.

Results

We noted a significant interaction between treatment response and changes in motor cortex excitability during active rTMS. Specifically, clinical improvement was associated with an increase in intracortical inhibition, intracortical facilitation and a prolongation of the cortical silent period. These results indicate that intraindividual changes in cortical excitability may serve as a correlate of response to rTMS treatment.

Conclusion

The observed alterations of cortical excitability suggest that low frequency rTMS may evoke long-term-depression like effects resulting in an improvement of subcortical inhibitory function.

Arm function after stroke: Neurophysiological correlates and recovery mechanisms assessed by transcranial magnetic stimulation

Transcranial Magnetic Stimulation has been used for over 20 years to investigate recovery of motor function in stroke patients. In particular, it has been used to quantify the extent of damage to the corticospinal output, reorganisation of the cortical representation of the affected body parts and excitability of intracortical and cortico-cortical circuitries in both hemispheres. In this review, we provide a detailed account of most of the published data with particular reference to methodological issues that affect their interpretation.

Motor cortex excitability after thalamic infarction

OBJECTIVE

We examined 8 patients with hemihypesthesia due to an ischemic thalamic lesion to explore the effects of a central sensory dysfunction on motor cortex excitability.

METHODS

Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Motor function was evaluated by the Nine-Hole-Peg Test and measurement of hand grip strength. The affected side was compared with the non-lesioned side and with an age-matched control group.

RESULTS

Patients had a loss of inhibition and an increase of facilitation in the motor cortex of the affected side. The silent period was prolonged and motor function was impaired on the affected side.

CONCLUSIONS

A thalamic lesion can modulate motor cortical excitability.

SIGNIFICANCE

This study suggests that, under normal conditions, somatosensory afferents influence inhibitory and excitatory properties in the motor cortex.

Motor excitability in a patient with a somatosensory cortex lesion

OBJECTIVE

We report a patient with an ischemic lesion in right somatosensory cortex who developed dystonic posturing and pseudo-athetotic involuntary left-sided finger movements during voluntary muscle contractions.

METHODS

Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Results obtained from abductor digiti minimi muscles of both hands were compared.

RESULTS

On the affected side, silent period duration and intracortical inhibition were reduced, indicating a loss of inhibitory properties. Intracortical facilitation was enhanced. Stimulus-response curves showed a smaller increase of motor evoked potential amplitudes when recorded during muscle relaxation, but not during voluntary muscle activation.

CONCLUSIONS

The results suggest that, under normal conditions, somatosensory cortex modifies inhibitory as well as excitatory properties in the motor system.