Temporal and spatial patterns of cortical activation during assisted lower limb movement.

Human gait is a complex process in the central nervous system that results from the integrity of various mechanisms, including different cortical and subcortical structures. In the present study, we investigated cortical activity during lower limb movement using EEG. Assisted by a dynamic tilt table, all subjects performed standardized stepping movements in an upright position. Source localization of the movement-related potential in relation to spontaneous EEG showed activity in brain regions classically associated with human gait such as the primary motor cortex, the premotor cortex, the supplementary motor cortex, the cingulate cortex, the primary somatosensory cortex and the somatosensory association cortex. Further, we observed a task-related power decrease in the alpha and beta frequency band at electrodes overlying the leg motor area. A temporal activation and deactivation of the involved brain regions as well as the chronological sequence of the movement-related potential could be mapped to specific phases of the gait-like leg movement. We showed that most cortical capacity is needed for changing the direction between the flexion and extension phase. An enhanced understanding of the human gait will provide a basis to improve applications in the field of neurorehabilitation and brain-computer interfaces.

Asymmetry of cortical activation during maximum and convenient tapping speed.

An effect of finger tapping rate on the hemodynamic response in primary motor cortex and the cerebellum has been well established over the last years (the rate effect). The present study compares the magnitude of this effect when either the dominant or subdominant hand is used by right and left handers. In contrast to previous studies maximum and convenient tapping rate for both hands are used as tapping tasks. The results confirm "rate effects" for the primary motor cortex and the cerebellum. In addition, a "rate effect" was found for the cingulate motor area. A novel finding is that the cortical and cerebellar "rate effects" are similar for the subdominant and for the dominant hand even though tapping rates are lower for the subdominant hand. This result demonstrates that the subdominant motor cortex and neurally connected cerebellar areas operate at suboptimal control levels although maximum neurophysiological activation has been reached during the maximum tapping task.

Extensive training of elementary finger tapping movements changes the pattern of motor cortex excitability.

There is evidence of a strong capacity for functional and structural reorganization in the human motor system. However, past research has focused mainly on complex movement sequences over rather short training durations. In this study we investigated changes in corticospinal excitability associated with longer training of elementary, maximum-speed tapping movements. All participating subjects were consistent right-handers and were trained using either the right (experiment 1) or the left thumb (experiment 2). Transcranial magnetic stimulation was applied to obtain motor evoked potentials (MEPs) from the abductor pollicis brevis (APB) muscle of the right and the left hand before and after training. As a result of training, a significant increase was observed in tapping speed accompanied by increased MEPs, recorded from the trained APB muscle, following contralateral M1 stimulation. In the case of subdominant-hand training we additionally demonstrate increased MEP amplitudes evoked at the right APB (untrained hand) in the first training week. Enhanced corticospinal excitability associated with practice of elementary movements may constitute a necessary precursor for inducing plastic changes within the motor system. The involvement of the ipsilateral left M1 likely reflects the predominant role of the left M1 in the general control (modification) of simple motor parameters in right-handed subjects.

Division of the corpus callosum into subregions.

Various attempts have been made to subdivide the corpus callosum (CC) into anatomically and functionally distinct subareas. A promising current approach is the use of factor analytic techniques in conjunction with traced MRI images. The traced images are divided into 99 percentile slices, where the widths of the percentile slices are used as variables that are entered into the analysis (Denenberg, Kertesz & Cowell, 1991). Studies that use this technique agree broadly between 6 and 7 factors, but available factor solutions contain inconsistencies and large gaps, which arise when many of the percentile slices do not load appreciably on any of the factors. The present study uses a larger number of brains (N = 184), all normalized, and some methodological refinements in the analysis of the traced MRI images of the CC. A stable 7 factor solution was found, and the factor structure for males and females was very similar.