Multisensory Environment for Neurophysiological MonitoringGregory Apker1, Vern Huang1, Nazriq Lamien2, Andrew Lin1,2, Emma Sirajudin2

Advisors: Daniel Polley, Ph.D.3, Mark Wallace, Ph.D.3

1Department of Biomedical Engineering, Vanderbilt University, Nashville, TN2Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN3Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN

PL 127.10  

Operating voltage [V] 0 - 60

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