Seth Horowitz
Assistant Professor of Neuroscience (Research):
Bio Med Neuroscience
Phone:
My research focuses on the development, adaptation, and interaction between different sensory systems in aquatic and terrestrial vertebrates. I use behavioral, physiological, anatomical and molecular techniques to explore how animals create and interact with the world of their senses. I've worked with dolphins, bats, rodents, frogs, and the occasional human, and am continually amazed at the similar mechanisms these species use to deal with their radically differing habitats and lifestyles.
Interests
My work focuses on several major areas in neuroscience and neuroethology, with a great deal of crossover and filling in the gaps between them. These areas include underwater and atmospheric hearing, auditory and vestibular development, biosonar in echolocating bats, interactions between the vestibular and other sensory systems, as well as balance and sleep interactions with a focus on microgravity applications. I also work with human responses to auditory (sound and music) and vestibular phenomenon.
Bioacoustics:
I started out studying dolphin behavior, studying changes in aggressive behavior among captive dolphins that emerged when they were exposed to different acoustic environments. While a simple study, it got me hooked on studying underwater hearing, particularly in areas that there had been little research before.
In my graduate work I studied underwater and atmospheric hearing in adult bullfrogs using both field and laboratory techniques. I have continued work in this area and in the biophysics of acoustic calling in general (Hainfeld et al, 1996; Boatright-Horowitz et al, 1999; 2000). I extended the scope of this work by examining changes that occur in the frog auditory system across metamorphosis and postmetamorphic development (Boatright-Horowitz& Simmons, 1995). My dissertation research was the first comprehensive study of auditory function and changes in central auditory neuroanatomy across the entire span of metamorphosis. Using anatomical and immunohistochemical techniques, I determined that the peripheral acoustic pathways of the tadpole and frog were substantially different (Horowitz et al, 2001). While even the youngest stage tadpoles showed highly sensitive underwater hearing, particularly at a higher frequency range than the adults, there is a brief transient "deaf period" when the tadpole is changing from a fish-like hearing system to a hearing system adapted to hearing in air. Furthermore, during this brief deaf period, there is a period of substantial neural reorganization of the central auditory system, although whether this reorganization is due to a Hebbian mechanism based on reduced auditory input, or convergent and independent developmental signals remains unknown (Boatright-Horowitz & Simmons, 1997). I continued this work by characterization of the midbrain coding of amplitude-modulated signals (Boatright-Horowitz et al, 1999) and in extensive analyses of afferent and efferent pathways linking the auditory brainstem to the midbrain (Horowitz et al, 2006).
Echolocation:
My postdoctoral work included computational modeling of atmospheric echolocation, using the Spectrogram Correlation and Transformation (SCAT) model of the echolocation system of the bat. The SCAT model provides biologically relevant data on the types of processes underlying some of the extraordinary temporal acuity available to echolocating FM bats, which may allow them to form three-dimensional (3D) acoustic images of objects. My work on the model focused on expanding its applicability for object detection, recognition, and classification as well as comparing its performance against other existing classification models for use in underwater object detection technology for the U.S. Navy.
Once I became more familiar with bat echolocation, I realized that there were major gaps in our understanding of how these animals actually used echolocation in the context of real-world flight and object detection. I became particularly interested in examining interactions between the echolocation and vestibular systems of echolocating bats, which hunt largely under conditions when there is little or no visual information available. I carried out a series of experiments involving 3D modeling of videotaped bat flights through complex static and rotating arrays. Flights were carried out under different lighting conditions or in darkness, in order to control for the contribution of different modalities, different degrees of echolocation complexity (rotating vs. static arrays) and different degrees of vestibular challenge through the use of a known nystagmic exaggerator, deuterium oxide (D2O). The results from this study indicate that while bats are capable of complex flight and orientation by echolocation alone, they will utilize visual cues when available. Furthermore, bats with D2O challenged vestibular systems showed substantially reduced flight success under complex echolocation environments (Horowitz et al, 2004).
Some of my current work at Brown University uses 3D modeling techniques to examine cross-modal sensory phenomena in echolocation. Current models of echolocation focus on the presence of specular acoustic surface reflections or "glints" as the perceptual cues that provide information about object distance and geometry. Using 3D modeling techniques for visual animation, I developed models of common real-world elements that can be detected by bat biosonar and mapped acoustic reflectivity data from natural and artificial targets onto luminosity, specularity and reflection coefficients for materials. This has allowed me to generate 3D visual animations of echolocation auditory scenes. Based on these animations, human observers are able to integrate object shapes, sizes, and movements based on gestalt grouping, particularly when the target moves or the echolocation source is moving in relation to the target. These types of modeling tools may help elucidate the perceptual phenomena arising from integration of the individual acoustic glint structures that allow bats and other echolocating animals to create complex umwelts from auditory data. A paper on this model is in preparation.
Vestibular-sleep interactions:
My work at Stony Brook University involved anatomical, molecular, and behavioral interactions between the vestibular and circadian systems. While photic input is a powerful modulator of the circadian clock, non-photic stimuli are capable of modulating circadian rhythms via geniculohypothalamic tract (GHT) projections from the intergeniculate leaflet (IGL) to the suprachiasmatic nucleus (SCN). Several lines of evidence indicate that circadian rhythmicity might be influenced by head motion or visual stimuli that affect the vestibular system. To examine potential effects of vestibular stimulation on circadian function, I carried out work on the golden hamster (Mesocricetus aureus) examining the effects of vestibular stimulation on components of the hamster circadian system. The anatomical work focused on choleratoxin, PHAL and gfp-conjugated Bartha-strain pseudorabies virus tract tracing work. This study established the presence of a monosynaptic projection from the medial vestibular nucleus to the IGL, as well as polysynaptic pathways to the SCN and identified numerous intermediary nuclei connecting the systems that are implicated in arousal and sleep behavior (Horowitz et al, 2004). Additional anatomical work demonstrated mono- and polysynaptic routes from the medial vestibular nucleus to a wide variety of nuclei directly involved in sleep regulation, including interactions with the orexin (hypocretin) network, a system critical for maintenance of arousal (Horowitz et al, 2005). I also demonstrated that vestibular stimulus-specific FOS expression was detected in these anatomical sites following mediolateral vestibular stimulation at specific times of day under dark conditions; however, while changes in motor behavior and sleep were noted based on differences in degree of vestibular stimulation, there were no obvious circadian phase shifts. The data suggest that at low vestibular frequencies, arousal is decreased and sleep may be induced utilizing a "Sopite" mechanism. With transient or high frequency/amplitude stimulation, an animal can be aroused from sleep. This suggests that there may be a psychophysical curve for sleep modulation based on vestibular input.
Multimodal integration:
I intend to focus my future research on the interactions between sensory modalities with an integrated systems approach. I have become extremely interested in the complex interactions that the vestibular system has with almost every other sensory and motor system, beyond the well studied oculomotor and postural/locomotor functions. I am beginning work on the development of vibratory sensitivity in the frog based on underwater particle motion sensitivity in tadpoles. Given the multiple homologies that exist between amphibian and other vertebrate models, I would like to expand these studies into mammalian studies, including human clinical studies. I also intend to pursue the cross-modal modeling techniques in order to continue exploring the role of higher order cognitive processing in both bat and dolphin echolocation. This area could not only provide critical next steps in our understanding of sensory integration across modalities, but it could also have profound implications for development of immersive simulations and virtual reality technologies.
Awards
1996 Brain & Behavior Graduate Fellowship, Brown University
1993 National Science Foundation (NSF) Graduate Fellowship
1992 Brown University Graduate Fellowship.
1992 National Institute of Mental Health Grad. Student Present. Award, 3rd Int'l Congress on Neuroethology, Montreal, Quebec.
1991 David L. Klein Memorial Scholarship for Graduate Study
1991 Livingston Welch Award for Psychological Research
1991 Deans Award for Academic Excellence, CUNY
Affiliations
Acoustical Society of America
Society for Neuroscience
New York Academy of Sciences
Funded Research
2005- National Institutes of Health/ National Institute on Deafness and Other Communication Disorders (NIH/NIDCD) 5R01DC005257-12: Neuroethology of Vocal Communication, A. Simmons, PI. S. Horowitz Co-PI
2001-2005 NSBRI NCC958155: Circadian and Vestibular System Relationships, L. P. Morin, P.I. S. Horowitz Co-P.I.
2000 Deafness Research Foundation: Development of the peripheral and central vestibular systems. P.I.
2000 R.I. Space Grant: Molecular characterization of vestibular nerve regeneration, A. Simmons, PI. Co-P.I.
1998 R.I. Space Grant: Development of vestibular system in anuran amphibians across metamorphosis. P.I.
1997 R.I. Space Grant: Interaction between echolocation and vestibular systems in the microchiropteran bat, E. fuscus.