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.

人工耳蜗是一种通过电刺激听神经来治疗耳聋的装置，由于人工耳蜗的神奇成功，对神经假体可行性的研究获得了动力。在今天的焦点中，由于许多神经系统疾病的特征在于中枢损伤，因此不能通过作用于周围神经系统的装置进行治疗，因此，神经外科医生感兴趣的是使用刺激大脑中枢部分（“中枢神经假体”）的方法。然而，在中央机器大脑接口处的数据传输遇到了一系列问题，这些问题在刺激外周神经的程度上是未知的。一个重要的问题是，传递函数，即刺激模式到神经元活动的转换是复杂的空间和时间的非线性相互作用，并且传递函数最有可能随着目标结构的功能状态而动态变化。第二个问题是，受试者对给定电诱发活动模式的可解释性的约束是未知的。本建议建立在先前描述的“主动”和“被动”触摸之间的转换，这两种功能状态在大鼠初级躯体感觉皮层（“桶皮层”）的胡须代表中，以接近这两个交织在一起的问题。当动物进行探索性的触须运动以获取触觉信息时，假定“主动触摸”状态，而“被动触摸”的特征在于触须静止时的触觉输入。触觉信号的不同幅度和传播以及桶皮层的背景活动速率是功能转换的标志。本提案旨在系统地评估在机器-大脑接口处的信号传输的特性（使用基本电刺激，如单脉冲和双脉冲，以及刺激的复杂时空模式）及其在主动和被动触摸的两个明确定义的功能状态中由受试者的可解释性。方法的工具包括新开发的技术相结合的多电极刺激和记录，心理物理测量的刺激检测和歧视，并在清醒的，头部固定的大鼠跟踪胡须运动。

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.