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Multisensory Environment for Neurophysiological Monitoring
Gregory
1
Apker ,
1
Huang ,
2
Lamien ,
1,2
Lin ,
Vern
Nazriq
Andrew
Emma
3
3
Advisors: Daniel Polley, Ph.D. , Mark Wallace, Ph.D.
1Department
2
Sirajudin
of Biomedical Engineering, Vanderbilt University, Nashville, TN
2Department
of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN
3Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN
Introduction
System and Environment
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.
Objectives
• 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
Engineering Tasks
• Update and repair of existing hardware components
• Increase usability/durability of system components
• Install environment hardware and architecture
Fig. 2: Rack-mounted DSP hardware (left), animal
sound chamber (center), PC (right)
Somatosensory Stimulator
PL 127.10
Operating voltage [V]
Nominal displacement [µm] ±20%
Free length [mm]
Dimensions L x W x T [mm]
Blocking Force [N]
Electric Capacitance [µF] ±20%
Resonant Frequency [Hz]
0 - 60
X
900
27
31.0 x 9.6 x 0.65
1
2 x 3.4
380
Fig. 3: Piezoelectric bending actuator characteristics
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
Fig. 4: DSM VF-500 linear amplifier, Flexbar® articulating arm
Data Analysis
• Implementation of wireless transmitter-receiver system
• Manage frequency range, spectral fidelity, and channel crosstalk
impact
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
Conclusions
• 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
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 piezoactuator, 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
Fig. 1: Block diagram of system control and operation
• 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
System Operation
Fig. 5: Spike sorting with wavelet analysis
Fig. 6: Example of analysis in frequency domain
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.