Cortico-cortical networks in patients with ideomotor apraxia as revealed by EEG coherence analysis

Abstract

We sought to determine whether coherent networks which circumvent lesioned cortex are seen in patients with ideomotor apraxia (IMA) while performing tool-use pantomimes. Five normal subjects and five patients with IMA (three patients with corticobasal degeneration and two with left hemisphere stroke) underwent 64-channel EEG recording while performing three tool-use pantomimes with their left hand in a self-paced manner. Beta band (20-22 Hz) coherence indicates that normal subjects have a dominant left hemisphere network responsible for praxis preparation, which was absent in patients. Corticobasal degeneration patients showed significant coherence increase between left parietal-right premotor areas. Left hemisphere stroke patients showed significant coherence increases in a right parietofrontal network. The right hemisphere appears to store useable praxis representations in IMA patients with left hemisphere damage.

Figure 1

Time-magnitude plots of individual (stroke) and mean coherence (normal subjects) divided into each network of interest relative to movement onset (s). Standard error bars represent the distribution of normal subject coherence. Asterisks (*) indicate significant increases, † denotes significant decreases.

Figure 2

Head plots of coherence relative to left and right premotor cortex in normal subjects (A), stroke patient #2 (B) and CBD patient #3 (C). A, B, and C (top) shows coherence relative to the electrode over the left premotor cortex. A, B, and C (bottom) shows coherence relative to the electrode over the right premotor cortex. Time (s) is relative to EMG onset. Coherence increases are shown in red; decreases in blue.

Figure 3

Time-magnitude plot of individual coherence values for patients with CBD for each network of interest for all participants relative to movement onset (s). Asterisks (*) indicate significant increases.