| An integral part of motor behaviour is the execution of sequential movements. Anatomical tract-tracing studies support the existence of recurrent neural pathways, from the motor cortex to the thalamus via basal ganglia, involved in motor behaviour. Although neuronal responses during sequential tasks have been examined in some detail at the level of the motor/premotor cortex, little is known about the responses at subcortical levels, particularly in the motor thalamus and subthalamic nucleus (STN). Stereotactic neurosurgery for implanting deep brain stimulating (DBS) electrodes provided a unique opportunity to examine single and double microelectrode recordings in the STN and motor thalamus in parkinsonian, chronic pain, and other movement disorders patients. 49 STN and 52 thalamic neurons were tested during internally and externally generated visually guided sequential reaching tasks. There were no differences between movement parameters (reaction time and movement time) amongst the tasks. Phasic and tonic responses were found in the STN with no preference for internally or externally generated reaching. The thalamic cells also displayed phasic and tonic responses with the majority of neurons responding during both internally and externally generated reaching. However, thalamic cells also displayed delay period, phase specific, and preparatory activity. These results demonstrate the involvement of the subcortical structures in complex responses previously observed in cortical areas suggesting the interaction of cortical/subcortical regions during sequential movements. |
