Multisensory Environment for Neurophysiological Monitoring Gregory Apker 1, Vern Huang 1, Nazriq Lamien 2, Andrew Lin 1,2, Emma Sirajudin 2 Advisors: Daniel Polley, Ph.D. 3, Mark Wallace, Ph.D. 3 1 Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 2 Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN 3 Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN PL Operating voltage [V] Nominal displacement [µm] ±20%900 Free length [mm]27 Dimensions L x W x T [mm]31.0 x 9.6 x 0.65 Blocking Force [N]1 Electric Capacitance [µF] ±20%2 x 3.4 Resonant Frequency [Hz]380 Many studies have shown the existence of large-scale plasticity in the visual, somatosensory, and auditory cortices of the brain. In addition, other research has focused on achieving a better grasp of multisensory interactions. However, these areas of neurophysiological monitoring have a great deal of room for improvement. It is important to conduct these studies because they drive our understanding of pathologies and perception. The labs of Dr. Polley and Dr. Wallace are trying to address the limitations of these past studies by adding new functionality to their multisensory environments. Awake recording capabilities will allow the exploration of the behavioral significance of physiological plasticity, compared to its simple characterization through anaesthetized recordings. Furthermore, the refinement of sensory stimuli through its accuracy in location and time will more closely simulate a naturalistic environment, eliciting more realistic responses. The goal of our project is to create the tools, involving both hardware and software, necessary to make these improved multisensory environments. Introduction Development of multi-sensory environment hardware for use in neuronal response characterization in rats and cats Produce visual, auditory, and somatosensory stimulation Modulate location and intensity of stimulation Integrate hardware to receive and deliver information Development of environment specific software for closed loop control of the environment Allow user defined stimulation parameters Initiate coordinated sensory stimulation Record, associate, and organize system output Objectives Update and repair of existing hardware components Increase usability/durability of system components Install environment hardware and architecture Implementation of wireless transmitter-receiver system Manage frequency range, spectral fidelity, and channel crosstalk impact Ground-up development of somatosensory stimulator system Design stimuli delivery and mounting apparatus Offer precision and versatility in application without confounding artifacts Integrate designed components Modification of existing in-lab software Increase functionality of Pre-Pulse Inhibition protocol Convert software from Visual Basic to Matlab Development of visual and auditory software Control delivery of sensory stimuli in time Collect, sort, and analyze data Engineering Tasks Comprehensive System PC defines and assigns experiment protocol to RX-6 DSP RX-6 DSP triggers stimuli presentation in the animal chamber Transducers in the animal chamber transmit data back to RX-6 RX-6 buffers and sends data to PC at periods allotted by the protocol PC saves data; post-analysis is later performed on the PC Somatosensory Stimulator A piezoelectric bending actuator was chosen due to its precise kinetic performance and its controllability The stimulator system is comprised of a linear amplifier, the piezo- actuator, and a securable, articulating arm to suspend the actuator above the animal subject A trapezoidal input wave produces controlled flexion (bending) along the piezoelectric beam Software initiates the input signal in precise coordination with auditory and visual stimulation The amplifier provides the ±30 V (60 RMS) needed to produce the bending/touching motion Multisensory Software Consists of three parts: visual, auditory, and somatosensory Visual: user inputs the locations of visual objects into software to have them displayed on the screen before the animal and to have the activity of neurons recorded Auditory: user sets the location of where the noise is played from the speakers to have the activity of neurons recorded Somatosensory: software controls the somatosensory probe, sets the parameters (time, pressure), and records the output Spike Sorting Real-time capture and sorting of neuronal response Characterizes multiple spikes into different classes that correspond to different neurons Stores and organizes the information of the characteristics of the neuronal response Forward Masking Tuning curves are complex enough to have to be done subjectively by a person Blurring and averaging options visually aid the operator Based on operator input, more statistics are formed to better delineate masking changes System Operation Fig. 5: Spike sorting with wavelet analysis Fig. 6: Example of analysis in frequency domain Data Analysis Conclusions The PPI protocol triggers stimuli consistently and stores data at rates within processor limits. Its GUI controller has options to allow hearing threshold testing in various scenarios. The stimuli hardware has been electrically upgraded for reliability. The piezoelectric bending actuator system successfully meets all of the crucial characteristics required for the somatosensory stimulation in the designed protocol. It is able to deliver a precise and controllable touching force and also offers complete freedom of motion and precision in placement. The Spike Sorting program accurately differentiates neural signatures. The complex analysis of frequency thresholds has been achieved in the Forward Masking program. It offers the user many visual aids and performs many backend data processes to allow seamless workflow. X System and Environment Fig. 4: DSM VF-500 linear amplifier, Flexbar® articulating arm Fig. 3: Piezoelectric bending actuator characteristics Somatosensory Stimulator Fig. 2: Rack-mounted DSP hardware (left), animal sound chamber (center), PC (right) Fig. 1: Block diagram of system control and operation