Oculomotor phenomena in petit-mal.

OBJECTIVE: To determine the temporal relationship among behavior, eye movements and respiration during absence seizures. METHOD: This included simultaneous videorecording of a patient's face, EEG and respirogram, in 5 patients with absence seizures. Absence seizures were defined as a sudden lapse of consciousness with impairment of mental functions. Oculomotor phenomena consisted of: eye fluttering, eye deviation (conjugate lateral or upward deflection), and eye-opening. RESULTS: Oculomotor phenomena began 1 2/3-3 s after the onset of the electrographic discharge and ended before the discharge. The most frequent events were eye-opening, stare with or without palpebral myoclonias, and tonic or clonic upward movements. Downward movement or convergence was not observed as well as head version. Respiratory changes (apnea) are the last events to occur. CONCLUSIONS: absence seizures were characterized by the onset of a 3/s spike-slow wave discharge followed by oculomotor phenomena and respiratory changes. The time course suggests that epileptic discharges precede and then involve oculomotor and respiratory brainstem centers.

Motor cortex inhibition is not impaired in patients with Alzheimer's disease: evidence from paired transcranial magnetic stimulation.

Motor cortex excitability was studied by transcranial magnetic stimulation (TMS) in 17 patients with Alzheimer's disease (AD). Resting and active thresholds for TMS were significantly reduced in AD patients compared to young and aged healthy subjects. The maximum amplitude of the motor response evoked by TMS was also significantly increased in AD patients. We have tested if these changes are related to a modification of the short-lasting intracortical inhibition of the motor cortex by paired conditioning-test TMS. We found no significant differences between AD patients and aged healthy subjects even if there is a slight but significant difference between aged and young normal subjects. We conclude that the modification of excitability of the motor cortex does not result from an impaired intracortical inhibition.

Corticomotoneuronal synaptic connections in normal man: an electrophysiological study.

In order to determine the mono- or oligosynaptic character of connections between pyramidal axons and individual spinal motor neurons, we constructed peri-stimulus time histograms (PSTHs) of the firing probability of voluntarily activated single motor units (SMUs) of various upper and lower limb muscles upon slightly suprathreshold transcranial anodal electrical stimulations of the motor cortex in normal subjects. Weak anodal cortical stimuli are known to activate preferentially fast-conducting pyramidal axons directly, bypassing cell bodies and cortical interneurons. A narrow bin width (0.1 ms) was chosen to measure precisely the duration of the PSTH excitatory peak, which corresponds to the rise time of the underlying compound excitatory post-synaptic potentials (EPSP). A short duration PSTH peak indicates sharp-rising EPSPs, most commonly encountered in the case of monosynaptic connections. In flexor carpi radialis and soleus SMUs, the PSTHs of built-in responses to anodal cortical stimuli were compared with those produced by 1A afferent stimulation able to elicit a Hoffmann reflex, which is known to be largely monosynaptic. In all upper and lower limb muscles, excitable SMUs responded to anodal cortical stimuli with a highly synchronized peak of increased firing probability. In flexor carpi radialis and soleus SMUs, the mean duration of this peak was significantly narrower than that evoked by 1A afferent stimulation, indicating that monosynaptic corticomotor neuronal transmission dominates low-threshold motor units, even in proximal arm and leg muscles. In the various muscles studied, and particularly in forearm SMUs, we did not observe broad PSTH peaks against the activation of non-monosynaptic corticomotor neuronal pathways, even with near-threshold stimuli. In some triceps and forearm flexor SMUs, subthreshold anodal pulses caused significant inhibition of their voluntary firing, with a latency consistent with activation of 1A inhibitory interneurons by the descending volleys. Measurements of the maximal number of counts in the excitatory PSTH peak upon anodal cortical stimuli provide comparisons of the strength of monosynaptic inputs to various muscles which seems to be maximal for hand and finger extensor muscles, and also for deltoid.