Modulation of motor learning by a paired associative stimulation protocol inducing LTD-like effects.

BACKGROUND: Paired associative stimulation (PAS) induces long-term potentiation (LTP)-like effects when interstimulus intervals (ISIs) between electrical peripheral nerve stimulation and transcranial magnetic stimulation (TMS) to M1 are approximately 21-25 ms (PASLTP). It was previously reported that two forms of motor learning (i.e., mode-free and model-based learning) can be differentially modulated by PASLTP depending on the different synaptic inputs to corticospinal neurons (CSNs), which relate to posterior-to-anterior (PA) or anterior-to-posterior (AP) currents induced by TMS (PA or AP inputs, respectively). However, the effects of long-term depression (LTD)-inducing PAS with an ISI of approximately 10 ms (PASLTD) on motor learning and its dependency on current direction have not yet been tested. OBJECTIVE: To investigate whether, and how, PASLTD affects distinct types of motor learning. METHODS: Eighteen healthy volunteers participated. We adopted the standard PAS using suprathreshold TMS with the target muscle relaxed, as well as subthreshold PAS during voluntary contraction, which was suggested to selectively recruit PA or AP inputs depending on the orientation of the TMS coil. We examined the effects of suprathreshold and subthreshold PASLTD on the performance of model-free and model-based learning, as well as the corticospinal excitability, indexed as the amplitudes of motor evoked potentials (MEPs). RESULTS: PASLTD inhibited model-free learning and MEPs only when subthreshold AP currents were applied. The PASLTD protocols tested here showed no effects on model-based learning. CONCLUSIONS: PASLTD affected model-free learning, presumably by modulating CSN excitability changes, rather than PA inputs, which are thought to be related to model-free learning.

The intensity of continuous theta burst stimulation, but not the waveform used to elicit motor evoked potentials, influences its outcome in the human motor cortex.

BACKGROUND: Responses to continuous theta burst stimulation (cTBS) applied to the human primary motor cortex are highly variable between individuals. However, little is known about how to improve the after-effects of cTBS by adjusting the protocol characteristics. OBJECTIVE: We examined whether current directions adopted in the measurement of cortical motor excitability indexed as motor evoked potentials (MEPs) affect the responses to cTBS. We also tested whether the stimulus intensity of cTBS influences the after-effects. METHODS: Thirty-one healthy volunteers participated. The after-effects of cTBS with the conventional intensity of 80% of individual active motor threshold (AMT) (cTBS80%) were tested by measuring MEP amplitudes induced by not only posterior-anterior (PA) but also anterior-posterior (AP) and biphasic (PA-AP) currents. We also investigated cTBS with 65% AMT (cTBS65%) and 100% AMT (cTBS100%) in subjects who showed depression of MEP amplitudes after cTBS80%, as well as cTBS65% in subjects in whom facilitation of MEPs was induced by cTBS80%. RESULTS: Current directions in MEP measurement had no influence on the cTBS responses. In subjects whose MEPs were depressed by cTBS80%, cTBS100% partly induced MEP facilitation, while cTBS65% abolished the after-effects. In subjects who showed MEP facilitation by cTBS80%, cTBS65% partly induced MEP depression. CONCLUSIONS: Stimulus intensity of cTBS influenced the responses to cTBS, and lowering stimulus intensity induced the expected after-effects of cTBS in some subjects.

Cardiac Asystole Triggered by Temporal Lobe Epilepsy with Amygdala Enlargement.

A 25-year-old previously healthy man was hospitalized for syncope. While standing, he suddenly lost consciousness, followed by a generalized tonic clonic seizure. An electrocardiogram demonstrated asystole. No cardiac abnormalities were detected on the echocardiogram, cardiac magnetic resonance imaging (MRI), positron emission tomography, or a coronary angiogram. An electrophysiological study showed normal sinus node and atrioventricular node function. An electroencephalogram revealed small spike waves in the fronto-temporal region. Brain MRI demonstrated a left-sided amygdala enlargement. To the best of our knowledge, this is the first case of temporal lobe epilepsy with an amygdala enlargement that induced cardiac asystole.

[A 53-year-old man with herpes encephalitis showing acceleration of improvement in higher brain function after general anesthesia with sevoflurane: a case report].

We experienced a right-handed 53-year-old man who presented with disturbance of consciousness and fever. Herpes simplex encephalitis (HSE) was diagnosed based on the detection of herpes simplex virus DNA in the cerebrospinal fluid. The administration of acyclovir for 42 days improved his consciousness level. Drowsiness, fever and seizures reappeared 20 days after stopping acyclovir treatment (day 67) and he responded well to vidarabine and methylprednisolone pulse therapy. An assessment of aphasia on day 98 revealed transcortical sensory aphasia. Brain MRI showed lesion in the left temporal lobe, bilateral insular cortexes and bilateral frontal lobe. His higher brain dysfunction continued. On day 156, he underwent hip replacement arthroplasty under general anesthesia sevoflurane. His higher brain dysfunction rapidly improved thereafter. We concluded that the accelerated improvement in our patient's higher brain function was related to the protective effect of sevoflurane. Some reports also show the protective effects of sevoflurane in experimental allergic encephalomyelitis by inhibition of T cell activation. These protective and anti-inflammatory effects may explain the accelerated improvement in higher brain function after general anesthesia.