1/4 XXII CBEB 2010 BRAIN TISSUE STIMULATOR FOR ELECTROPHYSIOLOGY AND NEUROFEEDBACK EXPERIMENTAL PROTOCOLS V.R.Cota*, L.E. Drumond**, M.F.D. Moraes** *DEPEB/UFSJ, São João Del-Rei, Brazil **NNC/ICB/UFMG, Belo Horizonte, Brazil e-mail: vrcota@ufsj.edu.br Abstract: Protocols using both recordings of biopotentials and electrical stimulation of brain tissue have been fundamental in experimental neuroscience, separately or as a set in neurofeedback system. Here we describe an electrical stimulator, which allows for configuration of all parameters through software, including current intensity. Performance of designed system was evaluated in a long term potentiation induction on amygdala slice preparation where electrical parameters were assessed. Overall our results show performance was satisfactory for a wide range of experimental protocols, including neurofeedback. Keywords: electrical stimulator brain neurofeedback Introduction Electrical stimulation (ES) is a useful technique in many experimental protocols in neuroscience, ranging from brain slices electrophysiology [1], long term potentiation (LTP) induction [2], behavioral modulation [3] to epileptic seizures suppression [4]. In a more recent investigation, simultaneous recording and ES in neurofeedback experiments brought novel possibilities to the study of neurosciences. This new framework turns possible previously unseen approaches for studying the physiology of the brain [5] and brings promising technologies for the treatment of neurological disorders [6]. This work describes an implementation of an electrical stimulator with all parameters controllable through software, which is a desirable feature in a neurofeedbak paradigm. Of note, we came up with a new solution for digital real-time control of current amplitude. The system is optically coupled for stimulus isolation, and has a 90 V output compliance powered by a simple 5 V supply. The design confers configuration flexibility suited for a wide range of experimental protocols. Material and Methods PC interface and configuration software We developed a C++ program to control all parameters of the stimulator. Basically, it keeps logical control of hardware configurations and sends digital commands through computer ports to set and reset them whenever desired. The 32 bits necessary for configuration were provided by digital I/O and multiplexing system. This PC interfacing solution is extensively described in electronics textbooks and in hobbyist magazines. The stimulator has two modes of operation: internal clock mode and PC clock mode. In internal clock mode the stimulation patterns are generated within the circuit itself, thus, being able to provide only ES patterns with fixed, yet programmable, frequency. In PC clock mode the stimulation patterns are generated by software that directly controls the firing of electrical pulses. In this case, virtually any temporal pattern of stimulus is possible. This mode could be used, for example, to induce LTP in amygdala slices, where a pattern of paired-pulses followed by three 1 second train pulses at 33 Hz is needed. Figure 1 - Block Diagram of the stimulator Overview of electrical stimulator hardware The tissue stimulator has seven main parts connected as depicted by the diagram of Figure 1: PC interface, power-supply, optical isolation, frequency clock, pulse clock, options management and output stage. Briefly, the frequency clock stage generates a 5 V square wave with programmed frequency that triggers the 1 st -pulse-clock at each negative-going border. This, in turn, generates a single-pulse of programmed width that will feed the options management system. Depending on the state of polarity control bit from PC interface, the options management system redirects the pulse to either output stages (positive or negative). If the number-of-phases bit is set high, implying biphasic pulse, options management system generates a trigger ISSN 2179-3220 1271