[P3-0799] Neural substrate for motivational control of descending motor pathways
キーワード：ventral tegmental area, primary motor cortex, motor output
【Purpose】
Positive emotion such as motivation is thought to boost motor performance whereas negative emotion such as depression is a psychological factor impeding rehabilitation therapy. It is believed that motivation is a key issue for enhancing the effect of rehabilitation therapy. Recently, we found that the ventral tegmental area（VTA）and the nucleus accumbens（NAc）, key components for processing of motivation, increased the activity in association with that of the primary motor cortex（M1）during recovery course from partial spinal cord injury in monkeys（Nishimura et al., 2011）. However, neural mechanism underlying such motivational effects on motor control remains unclear. The purpose of this study is to clarify how motivation-related areas affect the activity of motor-related area and motor control.
【Methods】
Data were obtained from two sedated macaque monkeys. Electrical stimulation was applied to the VTA or the NAc using bipolar electrodes. Evoked-responses in the electrocorticograms over the cortical areas ipsilateral to stimulation side and responses of upper limb muscles contralateral were recorded.
【Results】
VTA stimulation induced evoked-responses not only in the orbitofrontal cortex（OFC）but also in the M1. In addition, repetitive stimulation of VTA induced excitatory responses in upper limb muscles. In contrast, NAc stimulation induced only the OFC activity. These observations were common in two monkeys.
【Discussion】
The present study showed that VTA which is known to process motivation could modulate the M1 and muscle activities and demonstrated the possible neural substrates for motivational control of motor outputs. Previous studies showed that the VTA has direct projections to the M1（Gasper et al., 1992）. VTA stimulation might affect the M1 activity and the excitability of descending motor pathways via VTA-M1 pathway. These findings suggest that up-regulation of motivational state may be important for enhancing the efficacy of rehabilitation therapy.
Positive emotion such as motivation is thought to boost motor performance whereas negative emotion such as depression is a psychological factor impeding rehabilitation therapy. It is believed that motivation is a key issue for enhancing the effect of rehabilitation therapy. Recently, we found that the ventral tegmental area（VTA）and the nucleus accumbens（NAc）, key components for processing of motivation, increased the activity in association with that of the primary motor cortex（M1）during recovery course from partial spinal cord injury in monkeys（Nishimura et al., 2011）. However, neural mechanism underlying such motivational effects on motor control remains unclear. The purpose of this study is to clarify how motivation-related areas affect the activity of motor-related area and motor control.
【Methods】
Data were obtained from two sedated macaque monkeys. Electrical stimulation was applied to the VTA or the NAc using bipolar electrodes. Evoked-responses in the electrocorticograms over the cortical areas ipsilateral to stimulation side and responses of upper limb muscles contralateral were recorded.
【Results】
VTA stimulation induced evoked-responses not only in the orbitofrontal cortex（OFC）but also in the M1. In addition, repetitive stimulation of VTA induced excitatory responses in upper limb muscles. In contrast, NAc stimulation induced only the OFC activity. These observations were common in two monkeys.
【Discussion】
The present study showed that VTA which is known to process motivation could modulate the M1 and muscle activities and demonstrated the possible neural substrates for motivational control of motor outputs. Previous studies showed that the VTA has direct projections to the M1（Gasper et al., 1992）. VTA stimulation might affect the M1 activity and the excitability of descending motor pathways via VTA-M1 pathway. These findings suggest that up-regulation of motivational state may be important for enhancing the efficacy of rehabilitation therapy.