[Complete Brain-machine Interfaces and Plastic Changes in the Brain].

Brain-machine interfaces (BMIs) are artificial systems that control external devices or body muscles with signals generated by the neural activities of working brains. The BMIs currently under development can be divided into 2 types,i.e.,conventional (noninvasive) BMIs and complete (invasive) BMIs. Only the latter type of BMI can ultimately be used in the future. This paper describes some recent studies on invasive BMI using monkeys as subjects and discusses the progress of and problems revealed in these studies. The focus then shifts to plastic changes in neuronal activities caused by the BMIs. When a BMI is in use,the brain inevitably changes its own functions and structures in order to operate external devices more efficiently. Therefore,basic research on BMIs inevitably involves study on neural plasticity; such research is essential for further development of neurorehabilitation and for high performance of BMIs. This paper describes 2 recent pioneering BMI studies-one involving the rat motor cortex and the other involving the monkey primary motor cortex. Both studies revealed rapid and plastic changes in neuronal function during the period the animals were learning to operate external devices with the BMIs. The fact that the neuronal changes were caused by the contingency of neuronal activity and rewards emphasizes the significance of the neural-operant paradigm for research on neuronal plasticity in BMIs. The present paper describes a neural-operant experiment involving a recently developed high-performance BMI system and reports rapid and plastic changes in firing frequency and synchrony of the hippocampal neurons in both adult and aged rats. Finally,the paper suggests that complete BMIs can be developed by neuroscience research and should be able to unmask the enigmas of the neural code,brain-body interaction,and ongoing activity in the working brain.