Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
-
Transcranial magnetic stimulation has been used to study changes in central excitability associated with motor tasks. Recently, we reported that a finger flexion-extension task performed at a maximal voluntary rate (MVR) could not be sustained and that this was not due to muscle fatigue, but was more likely a breakdown in central motor control. To determine the central changes that accompany this type of movement task, we tracked motor-evoked potential (MEP) amplitude from the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles of the dominant hand in normal subjects for 20 min after a 10 sec index finger flexion-extension task performed at MVR and at a moderate sustainable rate (MSR) and half the MSR (MSR(/2)). ⋯ Measurements of short-interval cortical inhibition revealed an increase in inhibition after all of the finger flexion-extension tasks, with the MSR task being associated with the greatest degree of inhibition. These findings indicate that a demanding MVR finger movement task is followed by a period of reduced corticomotor excitability and increased intracortical inhibition. However, these changes also occur with and are greater with slower rates of movement and are not specific for motor demand, but may be indicative of adaptive changes in the central motor pathway after a period of repetitive movement.
-
To investigate the effects of homotopic and heterotopic conditioning pain modulation (CPM) on short-term cortical plasticity. Glutamate (tonic pain) or isotonic saline (sham) was injected in the upper trapezius (homotopic) and in the thenar (heterotopic) muscles. Intramuscular electrical stimulation was applied to the trapezius at pain threshold intensities, and somatosensory evoked potentials were recorded with 128 channel EEG. ⋯ A positive correlation at P300 between pain ratings to glutamate injection and the x coordinate during tonic pain (P = 0.016) was found for heterotopic CPM. Heterotopic CPM caused short-term cortical plasticity within the cingulate that was correlated to subjective pain ratings. The degree of long-term depressive effect to homotopic CPM was correlated to the change in location of the P200 dipole.
-
To investigate whether priming stimulation influences the responses of intracortical inhibitory and facilitatory motor circuits to a subsequent plasticity-inducing inhibitory theta burst TMS paradigm. Using standard transcranial magnetic stimulation (TMS) procedures, MEP amplitude, short-interval intracortical inhibition (SICI), and short-interval intracortical facilitation (SICF) were assessed at baseline and 5, 20 and 30 min following continuous theta burst stimulation (cTBS), intermittent TBS (iTBS), and iTBS-primed cTBS. SICI was assessed using paired-pulse TMS at inter-stimulus intervals (ISI) of 3 ms (SICI(3)) and the latency corresponding to the latency at which SICF was minimal in each individual. ⋯ Synapses mediating MEP generation undergo modification following iTBS-primed cTBS, possibly through mechanisms related to metaplasticity or synaptic depotentiation. A lack of substantial changes in SICI and SICF under all experimental conditions suggests that the tested rTMS paradigms may be non-optimal for inducing robust modulation of the neural elements mediating SICI and SICF across subjects. Priming stimulation may provide an approach which facilitate neuroplastic change within the human motor cortex at least in circuits responsible for MEP generation.
-
Repetitive transcranial magnetic stimulation (rTMS) has been studied increasingly in recent years to determine whether it has a therapeutic benefit on recovery after stroke. However, the underlying mechanisms of rTMS in stroke recovery remain unclear. Here, we evaluated the effect of rTMS on functional recovery and its underlying mechanism by assessing proteins associated with neural plasticity and anti-apoptosis in the peri-lesional area using a subacute cerebral ischemic rat model. ⋯ The rTMS group showed more functional improvement on the beam balance test and had stronger Bcl-2 and weaker Bax expression on immunohistochemistry compared with the sham group. The expression of NMDA and MAP-2 showed no significant difference between the two groups. These results suggest that rTMS in subacute cerebral ischemia has a therapeutic effect on functional recovery and is associated with an anti-apoptotic mechanism in the peri-ischemic area rather than with neural plasticity.
-
Case Reports Comparative Study
Neuronal discharge patterns in the globus pallidus pars interna in a patient with Parkinson's disease and hemiballismus secondary to subthalamotomy.
Alterations in the basal ganglia-thalamocortical "motor" circuit activity, have been proposed to explain many features associated with hypokinetic and hyperkinetic movement disorders. We describe the firing pattern of the globus pallidus pars interna in a Parkinson disease's patient who developed Hemichorea-Ballismus subsequent to ipsilateral subthalamotomy, and compare findings to those from PD patients submitted to pallidotomy while in the OFF-medication state. Single units obtained from extracellular recordings were extracted and mean discharge frequency, interspike interval and coefficient of variation (defined as Tonicity Score) were computed. ⋯ Mean firing frequency showed no significant difference between PD patients in the OFF state and the patient we report. However, a significant difference in tonicity was found for this patient characterized by a regular, non-bursting firing pattern. The findings indicate that in HB caused by lesions to STN in the parkinsonian state, GPi firing rates can be similar to and firing pattern more regular than those observed in GPi of PD patients OFF-medication with intact STN.