Context dependent changes of signal transfer at a central machine-brain interface. A study using mulitelectrode stimulation an d recording in barrel cortex of awake rats during active and passive touch.

点击翻译按钮获取中文摘要

Research on the feasibility of neuroprostheses has gained momentum from the miraculous success of the cochlea implant, a device which electrically stimulates the acoustic nerve to treat deafness. In the focus of today¿s interest are approaches using stimulation of central parts of the brain (`central neuroprostheses¿) because many neurological disorders are characterized by central lesions and therefore can not be treated by devices acting on the peripheral nervous system. Data transfer at a central machine¿brain interface, however, is met by a host of problems not known to this extent from stimulation of peripheral nerves. One important problem is that the transfer function i.e. the conversion of stimulus patterns into neuronal activity is complicated by non-linear interactions in space and time and that the transfer function most likely changes dynamically with the functional state of the targeted structure. The second problem is that the constraints governing the interpretability of a given electrically evoked activity pattern by the subject are not known. The present proposal builds on the prior description of a switch between `active¿ and `passive¿ touch, two functional states in rat¿s whisker representation in primary somatosensory cortex (`barrel cortex¿) in order to approach these two intertwined problems. The state of `active touch¿ is assumed when the animal performs explorative whisker movements to acquire tactile information while `passive touch¿ is characterized by tactile inputs while the whiskers are at rest. Different amplitude and spread of tactile signals as well as rate of background activity in barrel cortex are the hallmarks of the functional switching. The present proposal aims at a systematic assessment of the characteristics of signal transfer at a machine-brain interface (using basic electrical stimuli like single and double pulses, as well as complex spatio-temporal patterns of stimuli) and its interpretability by the subject in the two well defined functional states of active and passive touch. The methodological tools comprise newly developed techniques combining multielectrode stimulation and recording, psychophysical measurements of stimulus detection and discrimination, and tracking whisker movements in awake, head-fixed rats.