Discrimination of motor and sensory processing in human EEG by power and synchronization analysis

grantor: University of TorontoDo EEG-based measures show the same sustained changes throughout different motor behaviors or conditions of sensory stimulation as observed in fMRI studies? EEG was recorded as subjects performed a variety of motor and auditory tasks. Power and mean cross-correlation values analyzed over a "large time window" were calculated in the high alpha (10.5-13Hz), mid beta (18-24Hz), and gamma (30-40Hz) frequency bands. Intrasubject comparisons (one way ANOVA) of power values, and to a lesser extent of cross-correlation (0 phase-delay) values, distinguished neuronal activity associated with some behavioral states compared to others. Generally however, patterns for both "regional" power and synchronization did not uniquely identify specific behavioral conditions. Also, intersubject analysis (pooled data) showed no significant differences (one way ANOVA) in power or synchronization values among experimental paradigms, but did reveal basic trends inherent in cortical activity and EEG based measures.M.Sc

Effects of peripheral sensory input on cortical inhibition in humans

Cortical inhibitory systems play an important role in motor output. The motor cortex can be inhibited by intracortical mechanisms and by peripheral sensory inputs. We examined whether cortical inhibition from peripheral sensory input is mediated through previously identified intracortical inhibitory systems and how these inhibitory systems interact. Two types of intracortical inhibition were assessed by paired-pulse transcranial magnetic stimulation (TMS). Short-interval intracortical inhibition (SICI) was determined with a subthreshold conditioning stimulus (CS) followed by a test stimulus 2 ms later and long-interval intracortical inhibition (LICI) with suprathreshold conditioning and test stimuli 100 ms apart. Cortical inhibition from peripheral sensory input was induced by median nerve stimulation (MNS) of the right hand and followed by a suprathreshold TMS over the left motor cortex 200 ms later. The first set of experiments tested the effects of different test stimulus intensities on SICI, LICI and cortical inhibition induced by median nerve stimulation (MNSI). With higher test stimulus intensities, LICI and MNSI decreased whereas SICI showed a trend towards an increase. The extent of SICI, LICI and MNSI did not correlate. The second experiment assessed the interaction between MNSI and LICI. The results of applying MNSI and LICI simultaneously were compared with MNSI and LICI alone. MNSI was virtually abolished in the presence of LICI and LICI was also significantly decreased in the presence of MNSI. Thus, the effects of MNSI and LICI when applied together were much less than their expected additive effects when applied alone. The degree of interaction between MNSI and LICI was related to the combined strength of MNSI and LICI but not to the strength of LICI alone. The third experiment investigated the interaction between SICI and MNSI. MNSI and SICI were applied together and the results were compared with MNSI and SICI alone. SICI remained unchanged in the presence of MNSI. We conclude that MNSI is mediated by circuits distinct from those mediating LICI or SICI. The MNSI circuits seem to have an inhibitory interaction with the LICI circuits, whereas the SICI and MNSI circuits do not seem to interact