Supplementary and presupplementary motor area involvement in conscious motor tasks

As a general definition, the motor cortex includes three large areas: the primary motor area, the supplementary area, and the premotor area. Each area has considerable circuitry. Intracortical stimulation and recording electrodes have revealed stimulation of the primary motor area creates relatively focused contralateral muscle contraction (simplified). When the supplementary motor and premotor areas are stimulated, they create patterned bilateral muscle movements. The latter two areas are thought to be intricately involved in the planning and encoding of movement. Recent studies involving positron emission tomography (PET) have revealed all three areas active during movement, supplementary motor cortex activity prior to movement, and premotor area activation when imagining movement. Few studies yet in humans have examined neuronal activity in these regions by direct recording of neuronal discharge during conscious movements. In this study, we examined the activity of single neurons in the supplementary motor cortex and presupplementary motor area during conscious motor tasks. Recordings were carried out in four patients with intractable epilepsy who underwent implantation of intracranial electrodes in order to identify the seizure focus for potential surgical resection. All patients performed easy and difficult consciously commanded finger appositional tasks. For each of the respected areas, time, difficulty, and left/right hand movements were analyzed in relation to the significance of neuronal firing. Activity was recorded in 13 neurons in the supplementary motor area and 14 in the presupplementary motor area. For each area, up to 23% of the neurons in the supplementary motor area, and as high as 50% of neurons in the presupplementary motor area showed significant firing patterns (p = 0.05) in relation in the conscious movement performed. Our results with single neurons support the hypothetical functions of the supplementary and presupplementary motor areas in planning, encoding and executing conscious movement.