2003 — 2009 |
Gdowski, Greg Thomas |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Vestibulo-Spinal Influences On Reflex Performance @ University of Rochester
DESCRIPTION (provided by applicant): Postural reflexes are evoked and controlled by a variety of sensory inputs. The vestibulo-spinal (VS) pathways carry sensory vestibular signals to widespread regions of the spinal cord where they interact with motor nuclei to produce reflexive movement. The vestibulo-collic reflexes (VCR) are an important subset of postural reflexes that avert potential neck injury by reorienting the head during perturbations of the body. The neck motor nuclei involved in producing the VCR receive input from two distinct populations of VS neurons that are anatomically distinguished by the absence or presence of collateral projections to the oculomotor nucleus. We hypothesize that these two distinct VS populations are important in controlling both reflexive head movements and reflexive gaze shifts (combined eye and head). To test this hypothesis we will record the firing behavior of VS neurons located in the vestibular nuclei during reflexive, voluntary, and passive head movements in the awake squirrel monkey. The monkey will be seated on a vestibular turntable and will be permitted to produce different combinations of voluntary and reflexive head movements only in the plane of the horizontal semicircular canals. Responses during voluntary and reflexive head movements will be quantified with respect to the response during rotations when the head is not permitted to move with respect to the body. Secondary VS neurons will be orthodromically identified from the vestibular nerve and antidromically identified as projecting to the spinal cord. VS neurons projecting to the oculomotor nucleus will be identified by the presence of eye movement related signals in their firing behavior and by antidromic activation following stimulation of the oculomotor nucleus. The goal of these studies is to characterize the signal processing for each of the VS neural populations with respect to the different functional roles of the VCR. The signal processing will be quantified and related to behavioral goals of the reflex to determine functional roles of each pathway. The results of these studies are not only significant to our understanding of the sensory-motor control of head movements but are also globally applicable to the control of all vestibular postural reflexes because their mechanisms likely utilize similar neural processing strategies.
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2005 — 2009 |
Gdowski, Greg Thomas |
P01Activity Code Description: For the support of a broadly based, multidisciplinary, often long-term research program which has a specific major objective or a basic theme. A program project generally involves the organized efforts of relatively large groups, members of which are conducting research projects designed to elucidate the various aspects or components of this objective. Each research project is usually under the leadership of an established investigator. The grant can provide support for certain basic resources used by these groups in the program, including clinical components, the sharing of which facilitates the total research effort. A program project is directed toward a range of problems having a central research focus, in contrast to the usually narrower thrust of the traditional research project. Each project supported through this mechanism should contribute or be directly related to the common theme of the total research effort. These scientifically meritorious projects should demonstrate an essential element of unity and interdependence, i.e., a system of research activities and projects directed toward a well-defined research program goal. |
Spatial Interaction of Otolith Mediated Collic Reflexes @ University of Rochester
Project 2, Spatial interactions of otolith mediated collic reflexes (Gdowski, PI), asks how the vestibular signals arising from otolith endorgans, which detect horizontal and vertical acceleration, are used to activate neck muscles that reflexively reorient the head. Cervical injury affects 1 million U.S. lives annually, yet we are just beginning to understand how postural reflexes that evolved to protect the neck are controlled. Progress has been hampered, in part, because of the complexity of the neck musculature and its multiple functions in reorienting gaze and reflexively stabilizing the head with respect to the body. Vestibulospinal (VS) pathways are richly innervated by converging otolith inputs. The signals carried by the VS pathways bilaterally and reciprocally activate neck muscles during static tilts and linear translations of the body. We hypothesize that neck muscle activity will exhibit spatial tuning when combinations of tilt and translation are imposed on the body sequentially throughout 3-D space. We further hypothesize that the spatial tuning of neck muscles is causally related to the spatial tuning of responses of vestibulospinal neurons. To test these hypotheses experiments will be carried out in squirrel monkeys in which the electromyography (EMG) of neck muscles and neural activity of VS pathways are recorded. Different combinations of tilt and translation will be imposed on the body throughout 3-D space. Initial experiments will determine if specific groups of neck muscles exhibit spatial tuning during tilts and translations in different directions. The second set of experiments will determine if VS neurons, recorded in the vestibular nuclei, exhibit spatial tuned responses during tilts and translations in different directions. VS neurons will be identified physiologically by antidromic stimulation. In addition, neck EMG activity and VS neuron activity will be recorded simultaneously so that spike-triggered averaging (SpikeTA) can be used to identify functional relationships between neural discharge and EMG activity. The spatial tuning of each neck muscle will be compared to the collective spatial tuning properties of sub-populations of VS neurons identified as functionally-related to the neck muscle (identified through SpikeTA). This analysis will be used to determine if the spatially-tuned neck EMG activity are causally related to the spatial properties of VS pathways. In the final experiments, the head will be allowed to move in the direction of translation while the responses of VS neurons are recorded. The directions of translation will be chosen based upon direction that maximally activates the neuron. These data will used us to determine how otolith signals are modified during the execution of collic reflexes. The results of these experiments are significant to our understanding of how otolith signals influence the orientation of the head during normal activities such as locomotion.
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