Supplementary motor area: neuronal response to motor instructions

Abstract

1. Single-unit recordings were obtained from the supplementary motor area of the cerebral cortex of two monkeys during execution of learned movements 2. Monkeys were required to push or pull a cast attached to the right forelimb in response to a sudden perturbation delivered via the cast. An instruction as to the direction of the monkey's movement was delivered 2.5--5 s prior to the occurrence of the perturbation and correct performance, therefore, required the animal to develop a preparatory state prior to the perturbation. 3. Of many hundreds of neurons recorded, 201 exhibited instruction-induced changes of activity during the period intervening between the instruction and the perturbation-triggered movement. 4. In 94 neurons, effects of the instruction were differential depending on which of the two instructions was given, whereas in 107 neurons, effects were nondifferential. The latencies of the differential responses appeared to be shorter (starting as early as 140 ms after the instruction). 5. The magnitude of the instruction effects varied in parallel with development of enhanced motor skill as the monkeys gained more experience in responding to the triggering stimulus. 6. These observations substantiate the hypothesis that the supplementary motor area plays a part in modifying a sensory-triggered motor output.

Comparison of neuronal activity in the supplementary motor area and primary motor cortex

“…Neuronal activity related to motor preparation is found in both MI and SMA [2]. However, if the preparatory process is more complicated, SMA neurons but not MI neurons are involved [73]. Furthermore, when subjects were required to use either right or left hand, or both hands together, the SMA activity was found to be strikingly different [70,71].…”

“…When monkeys were prepared to push or pull a handle in response to a forthcoming movement-trigger signal, the difference of the intended movements was reflected in the preparatory activity of SMA neurons [73]. Namely, the neuronal activity increased or decreased during the preparatory period, depending on whether the animal was intending (but not initiating) to push or pull a handle.…”

“…It is important to know whether such preparatory activity in the SMA is transmitted to the MI. A partial answer to this question was obtained when SMA neurons exhibiting the preparatory activity was electrophysiologically identified to project to the MI [73]. It was also found that MI neurons having the preparatory type of activity receive inputs from the SMA, rather than from the thalamus or the parietal cortex [1].…”

Temporal Development of Anticipatory Reflex Modulation to Dynamical Interactions During Arm Movement

“…One of the possible brain areas is the supplementary motor area (SMA), which is thought to play a role in modifying responses to sensory inputs (Dick et al 1987;Hummelsheim et al 1986Hummelsheim et al , 1988Tanji et al 1980). Tanji et al (1980) showed instruction-dependent modulation of neural discharges to a mechanical stretch in the SMA, as observed in the M1 Tanji 1974, 1976). Hummelsheim et al (1986) showed that intracortical stimulation of the SMA had an inhibitory effect on responses of area 4 neurons to kinematic stimuli.…”

The Role of Dopamine in Normal Rodent Motor Cortex: Physiological Effects and Structural Correlates

“…Lesions to the SMA result in complex motor dysfunctions, including severe akinesia (Freund, 1987), and the inability to sequence complex motor tasks (Shima and Tanji, 1998). Electrophysiological studies show that SMA neuronal activity is tightly coupled with movement preparation (Tanji et at, 1980). Neurons in the SMA are active well in advance of movements (Alexander et at., 1990;Lang et aI., 1991).…”