Measurement automation to control brain-machine interfaces

The brain is one of the most temperature-sensitive organs in the human body, and this feature can be often linked to physiological phenomena and anomalies. Innovative state-of-the-art devices can investigate the neuronal response to temperature transients to assess, for instance, neurodegenerative diseases evolutions. For this purpose, implantable optical stimulation microdevices, or simply optrodes, have been designed by the Research Group of Implantable Microsystems, Pázmány Péter Catholic University, in collaboration with the Hungarian Academy of Sciences. The optrodes are multimodal devices; they simultaneously provide information on thermal and electrophysiological variations, as well as IR infrared light delivery into neural tissue, in a spatially controlled manner. In this master thesis project, optrodes have been adopted in order to implement a Matlab-based closed-loop control system. Moreover, a graphical user interface (GUI) has been developed to enable brain researchers to use the control system. Once the user has set up the necessary parameters, through the provided GUI, the user kickstarts the procedure. The control procedure begins with the 4-wire measurement of the optrode-integrated Pt filament sensor's resistance; this measurement is then converted into temperature values through the Callendar-Van Dusen relation. The temperature measurements are then used as control values for the control software, to decide whether IR irradiation by the optrode is required. Consequently, the IR irradiation causes thermal increase which continues to be monitored by the closed-loop system until any stop conditions are met. The light irradiation is performed through the communication between the software and a source-measure unit (SMU) which provides a DC supply current to an IR laser diode optically coupled to the optrode's Si waveguide, causing the IR light delivery from the microdevice tip. The achieved control system can adjust the DC supply current value according to the measured temperature in every loop cycle. In critical cases or in the presence of anomalies the system can: temporarily pause instruments communication automatically (e.g. tissue overheating prevention), exit from control loop and end instruments communication automatically (e.g. maximum laser diode's working current exceeding) as well as through the user action. All the design choices for the software realization benefit both from the literature analysis, particularly the research concerning rats neocortex IR irradiation as well as instrument specification datasheet and manuals. The design process has been clearly outlined, from measurements accuracy calculations to IR diode's supply current values assessment, in relation to the optical power provided. Furthermore, parameters choices concerning the correct SMU communication, expressed in LUA programme language, have been justified. The control system operation has been demonstrated by using tap water; thus, it aims to be a promising experimental tool to reveal thermal behaviour by way of self-adjusting control software.