INVOLVEMENT OF THE SUPPLEMENTARY MOTOR AREA IN VOLUNTARY CONTROL OF BREATHING

Voluntary control of breathing is a fundamental brain function involved in behaviors such as speech and singing. Although many neuroimaging studies have identified several cortical areas, including the supplementary motor area (SMA), as being related to this control (McKay et al., 2003), the underlying neuronal mechanisms remain unclear. In this study, we established voluntary control of breathing in macaque monkeys using an inhalation-timing task, in which monkeys were required to initiate an inhalation within either an early (100–1,500 ms) or a late (1,000–4,000 ms) time window to obtain a liquid reward. To investigate how the SMA mediates voluntary control of breathing, we recorded single neuron activity from the SMA in three monkeys during the inhalation-timing task. We found that neuronal activity during the early and late conditions differed from that observed during automatic breathing. Of the 360 neurons recorded in the left SMA, 80 (22.23%) showed increased activity during voluntary breathing, whereas only 30 of 442 neurons (6.79%) in the right SMA showed such increases. The majority of task-related neurons were thus located in the left hemisphere (p < 0.05). Furthermore, local inactivation of the left SMA impaired task performance in both the early and late conditions. These results suggest that the left SMA plays a dominant role in the voluntary control of breathing. It is known that language processing is predominantly regulated by the left hemisphere, the left SMA may also contribute to coordinating respiration with speech production.