Mark Wallace

Mark Wallace, Ph.D Laboratory Director

Director, Vanderbilt
Brain Institute

Overview

Development

Plasticity

Receptive Field Organization

Framework for Dyslexia

Multisensory Processes in Autism

Relevant Videos

Current Projects

Multisensory Training in Anesthesia Practice

Joe's FigureJoe's Figure 2

In acute care settings, the detection and response to clinical signals is critical to safe patient care. The design of audible and visual alarms has proven problematic in this regard; undue sensitivity or priority leads to excessive false alarms (and alarm fatigue) while, with insufficiently salient or sensitive alarms, critical events are missed. Studies suggest that clinical alarm design can be significantly improved by considering auditory and visual signals together as an integrated multisensory signal. I have created a unique experimental model to study the effects of the combined use of auditory and visual alarms on clinician detection and decision-making. I will use this model to study the dynamic responses of critical care clinicians performing multiple stimulus-response trials. The stimulus is an acute change in a visually presented vital sign and its associated audible alarm signal, presented on realistic ICU background sounds. Performance variables are response time and accuracy of a treatment decision. A secondary auditory task modulates attentional workload. I will examine the stimulus-response curves with: 1) Varying auditory signal-to-noise ratios and clinical scenario complexity and 2) Developing novel multisensory alarms to improve response time and accuracy to recognizing clinical deterioration and instituting therapeutic intervention. The results will inform recommendations for ICU alarm design to maximize performance while minimizing alarm fatigue.

Effects of Neurotransmitter Activity on Multisensory Processing

The integration of information across the senses is vital for our everyday interaction with the world. The superior colliculus (SC) is a critical brain region for these integrative processes. While much is known about how this process develops and how it occurs, less is understood about the neuromodulatory systems involved in the tuning of multisensory integration. I am interested in understanding the role of the serotonin (5-HT) system in the multisensory processing occurring within the SC. I utilize the methods of in vivo electrophysiology and pressure-injection of serotonergic compounds during single-unit recordings to determine the part the 5-HT system plays in shaping multisensory integration.

Behavioral and Neural Variability in Autism Spectrum Disorder

Sensory dysfunction is now recognized as a core symptom of Autism Spectrum Disorder (ASD), as well as restricted interests and repetitive behaviors, and deficits in social communication and interaction. In addition to atypical sensory response, performance on a number of sensory and motor tasks is not only worse, but also more inconsistent from trial to trial in individuals with ASD. A growing body of literature suggests that differences in behavioral variability, and its underlying neural correlates, may provide important clues about the encoding of sensory information and its transformation to behavioral output in ASD. Using both behavioral testing and neuroimaging with fMRI, the experiments carried out under the project aim to provide a thorough characterization of both behavioral and neural (i.e. BOLD) variability in ASD and TD children, and the associated effect of variability on speech processing abilities. Our second goal is to investigate the malleability of sensory processing through the use of a perceptual training paradigm with ASD individuals, aimed at decreasing variability and improving speech perception.

Multisensory Integration in Clinical Populations

Multisensory integration can be described as the merging and transformation of information from the different senses. Autism spectrum disorders (ASD) are complex neurodevelopmental disorders characterized by impairments in communication and social behavior as well as the presence of repetitive and restrictive behaviors. In addition to the classic domains impacted in autism, sensory abnormalities are also highly prevalent in ASD with the new DSM-V now including sensory disturbances as a criterion for diagnosis. Based on the wealth of evidence highlighting disturbances across multiple sensory systems, there has been increased focus on better characterizing how the integration of information across the different sensory modalities is impacted in autism. My project is focused on psychophysical, behavioral and systems based questions to gain a further understanding of the underlying mechanisms of multisensory processing as it relates to neurodevelopmental disorders such as autism with the ultimate goal of developing more effective remediation tools.

Multisensory Network Properties

My primary research interests focus on how the brain copes with sensory loss, particularly deafness, and the subsequent restoration of hearing, i.e. cochlear implants (CIs). Furthermore, I am interested what role multisensory networks may play during hearing loss and reinstatement. I postulate that other modalities may help overcome auditory deprivation and that subsequent to CI placement existing senses aid in instructing the newly arriving auditory signals. To investigate this, I am currently utilizing neurophysiological recording and neuroanatomical tract tracing techniques in order to characterize multisensory network properties in the normal brain with emphasis on corticocortical and thalamocortical loops. In the future, I would like to expand upon this work in the deaf brain. Here, I believe that identifying neurogenetic markers and physiological changes in network activity and comparing those findings to data from the normal brain would be of great value.

The neural underpinnings of multisensory behavior

My research project is aimed at understanding how multisensory neurons in the superior colliculus contribute to behavior. Non-human primates are trained to report the detection of auditory stimulus via manual response while being presented auditory, visual, and combined audiovisual stimuli. Behavioral responses simultaneously with neuronal activity so that a direct link between brain activity and behavior can be explored. Additionally, my research seeks to understand how stimulus factors such as intensity and the spatial and temporal relationships between the unisensory components of a multisensory stimulus affect behavior and the neuronal mechanisms responsible for that behavioral change

EEG Investigation of Sensory Processing Networks

My research interest is using Electroencephalography (EEG) to explore differences in sensory processing and brain networks in individuals with autism spectrum disorder (ASD).  Sensory dysfunction is a recognized primary component of ASD, but there is still a great deal we do not know about how the neural mechanisms of sensory processing are altered in individuals with ASD and how this leads to behavioral impairment.  Specifically in the multisensory domain, we know that individuals with ASD have a wider temporal window for integration of unisensory components as well as decreased behavioral facilitation in terms of reaction times.  My work centers on using the high temporal resolution of EEG combined with psychophysical approaches to determine how differences in sensory system activity lead to altered perception in individuals with ASD.  Additionally, through application of graph theory approaches of network modelling to EEG data I am investigating how disruptions in overall network properties, such as long range connectivity and modularity, are associated with perception in both ASD and typical development. 

_________________________________________________________

Past Projects

The Development of Multisensory Processes. Research in this area seeks to better characterize how multisensory circuits mature during early postnatal life. The approaches used for this work range from single neuron electrophysiology to psychophysics and event related potentials (ERPs) in children.

Experiential Plasticity in Developing and Adult Multisensory Circuits. Works seeks to better understand how early sensory experience shapes developing multisensory circuits, and the surprising degree of plasticity that can be enabled in adult representations.

Spatiotemporal Receptive Field Organization and Multisensory Integration. Ongoing research in the lab seeks to describe the complex receptive fields that characterize multisensory neurons in both cortical and subcortical structures, and to describe how this receptive field architecture influences the multisensory processing capabilities of these neurons.

A Multisensory Framework for Developmental Dyslexia. In prior work we have shown that alterations in multisensory temporal processes may be associated with the prevalent reading disability - developmental dyslexia. Current work seeks to extend this finding and better elucidate the affected brain circuits.

Altered Multisensory Processes in Autism Spectrum Disorder. New research in the lab seeks to better characterize sensory and multisensory processing in children with autism spectrum disorder.