Involvement of human thalamic neurons in internally and externally generated movements

Several anatomical studies support the existence of recurrent neural pathways from cortical motor areas to the thalamus via basal ganglia and back to the cortex. Neuronal responses to internally and externally generated sequential movements have been studied in the motor and premotor cortex of monkeys, but the involvement of subcortical motor structures such as the thalamus have not been studied in monkeys or humans. We examined the activity of neurons during a sequential button press task in motor thalamus of parkinsonian as well as chronic pain patients undergoing implantation of deep brain stimulating electrodes. Single and dual microelectrode recordings were carried out during an internally generated task with a memorized sequence (MEM) and an externally driven task with the sequence given during task performance (follow). Average histograms of neuronal firing were constructed for each task and aligned with respect to visual cues (ready, go) or button presses (P1, P2, P3). Sequential movements were monitored with surface electromyography and hand accelerometry, and cell responses were divided into movement-defined epochs for ANOVA and post hoc means testing. Of 52 neurons tested, 31 were found to have task-related responses and 10 were task-selective with 4 responding preferentially to MEM and 7 responding preferentially to follow (1 was both). Complex responses were found including preparatory, delay period, and phase- and task-specific activity. These kinds of responses suggest a role of the thalamus in both internally and externally cued arms movement and provide some evidence for a role in sequential movements.