Stanley J. Bolanowski, Jr. - US grants

The long-range goals of the project remain essentially unchanged from previous years, that is, to extend our understanding of the psychophysical characteristics of responses to vibrotactile stimulation in humans within the context of the possible receptor/neural mechanisms that may underlie those characteristics. Beyond these fundamental and basic goals, and in the realm of application, information processing by cutaneous tactile systems may be utilized when the effectiveness of conventional channels is limited, as in high noise environments, when existing channels are overtaxed, or when existing channels suffer a sensory deficit. There still exist sizable gaps in our knowledge of the fundamental characteristics of the cutaneous sensory systems and that knowledge lags far behind the information that is available for the auditory and visual systems. The basic aim of the proposed research is to close these gaps. The experiments fall into five general problem areas: 1) spatiotemporal aspects of vibrotactile sensation, especially those relating to the development of tactile communication devices; 2) further exploration of parameters relating to the newly developed four-channel model of cutaneous mechanoreception at threshold; 3) suprathreshold levels of stimulation; 4) cross-modality interactions; and; 5) effects of peripheral neuropathies associated with carpal tunnel syndrome, vibration "white finger", and diabetes. The experiments are targeted on exploring the functional properties of both Pacinian and non-Pacinian receptor systems, within the context of the four-channel model.

The auditory and tactile systems convert mechanical energy into neural activity for the purposes of perceiving our environment. This commonality suggest that the two sensory systems may use similar mechanisms for encoding stimulus intensity, but the manner in which this occurs is still unresolved for both systems. Furthermore although there are many similarities between these two systems, their peripheral organization is quite different. The experiments proposed in this subproject are designed to determine the basic morphology of certain aspects of the tactile system and to compare and contrast the organizing principles found in audition and taction. The experiments are designed to determine if differences in receptor design and spatial arrangement result in different schemes for intensity coding in the two systems, or if the systems are essentially similar despite the peripheral diversity. An additional goal is to determine the morphological substrates involved in tactile intensity coding and to relate these to the tactile psychophysical and physiological mechanisms. Thus a few of the long-range goals are to understand how tactile receptors encode stimulus intensity, how the peripheral nerve fibers that convey the result of transduction toward the brain are organized, and how the central structures that receive these nerve fibers are arranged for the neural processing of loudness. Using the cat as the animal model for humans, we will determine the organization of the peripheral nerves innervating the hairless (glabrous) skin and link the response properties of the peripheral nerve fibers to their anatomical endorgans. Furthermore we will test the hypothesis that the loci of transduction in tactile receptors are elements (filopodia) that project from the nerve fibers innervating the various endorgans. We will do this using well-established histological, biochemical, molecular-biological techniques, and electrophysiology. Lastly, enzymatic and mechanical removal of he Pacinian corpuscle's accessory capusle and attendant electrophysiology should reveal basic mechanisms of transduction of importance both for audition and taction. The results will provide a scientific rational for methods than can be used to devise treatments and prosthetic devices, to ameliorate partial or profound deafness, and to recruit the use of the tactile system as a surrogate input for auditory information.

The auditory and tactile systems convert mechanical energy into neural activity for the purposes of perceiving our environment. This commonality suggests that the two sensory systems may use similar mechanisms for encoding stimulus intensity, but the manner in which this occurs is still unresolved for both systems. Furthermore, although there are many similarities between these two systems, their peripheral organization is quite different. The experiments proposed in this subproject are designed to determine the basic physiology of certain aspects of the tactile system and to compare and contrast the organizing principles found in audition and taction. The studies are designed to determine if differences in peripheral nerve activity result in different protocols for intensity coding between the two systems, or if the systems are essentially similar despite the peripheral diversity. Another goal is to determine the mechanisms involved in tactile intensity coding, relating these to the tactile psychophysical phenomenon and morphological substrates. Thus one long-range goal is to understand how tactile receptors encode stimulus intensity and how the peripheral nerve fibers convey the information to central-nervous-system location. using the cat as the animal model for humans, we will determine the peripheral physiology in response to sinusoidal and complex stimuli and like the response properties to their anatomical endorgans. Furthermore, we will test the hypothesis the loci of transduction in tactile receptors are elements (filopodia) that project from the nerve fibers that innervate the various endorgans. We will do this using well-established physiological recording methods and electron microscopy. Lastly, enzymatic and mechanical removal of the Pacinian corpuscle's accessory capusle and attendant electrophysiology should reveal basic mechanisms of transductions of importance both for audition and taction. The results will provide scientific rational for methods that can be used to devise treatments and prosthetic devices, to ameliorate partial or profound deafenss, and to recruit the use of the tactile system as a surrogate input for auditory information.

Continuation of research on specific, long-range problems of intensity effects and processing in the auditory and tactile systems. The research has generated hypotheses and broad generalizations that require further testing. It has also produced substantial empirical information that requires further interpretation and integration. These results make additional experimentation and theoretical work necessary. A multidisciplinary approach is being used, including 1) human behavior, 2)neurophysiology, and 3) neuroanatomy, with the specific goal of providing definitive answers to still unresolved problems of transduction and intensity coding in the two sensory systems. Specific experiments within modalities run parallel and complementary courses; the six projects are interlocked in their goals. A systems-analysis approach will be used. Gloabla functions are determined from human psychophysics. Experiments focus on stimulus intensity, frequency and time parameters of intensity discrimination and on intensity effects in the discrimination of complex stimuli, and the correlation of behavioral and neural responses within the auditory system. Contributions of relevant components of the system to global functions are sought through direct physiological and morphological experiments. We will see to psychophysically explore the parameters of intensity discrimination in human tactile systems with the goal of relating global functions to the underlying physiological mechanisms and their morphological substrates. Some experiments concern the effects of stimulus intensity on the neural responses in the auditory periphery. Other experiments are focused on the effects of stimulus intensity upon neuron responses in the tactile periphery so that these may be related to sensory functions and morphology. There will be focus on the roles in transduction and intensity effects played by auditory hair cells, eighth nerve and cochlear nucleus, and correlates to components of the peripheral tactile system. We will also focus on receptor and fiber types in the peripheral tactile systems and attempts to elucidate their roles in transduction and intensity effects. Experiments involve humans as well as other vertebrate animals. All experiments are consistent with the expertise of a multidisciplinary team, and long-range goals of fundamental importance to understanding human perception and its underlying neural mechanisms. the information generated relates closely to the practical needs of the biomedical community.

DESCRIPTION (Adapted from the applicant's abstract): The sense of touch is pivotal to survival. When it is corrupted through disease, environmental and homeostatic conditions cannot be sensed, resulting in major physical, experiential and cognitive deficiencies. Furthermore, the sense of touch often becomes the surrogate aid for the deaf or blind, perhaps best exemplified by Braille. In spite of its importance for human survival, comparatively little is known about the sense of touch when compared to hearing and vision. Thus the long-term objective of the research program is to determine the underlying bases for somatosensory sensation and perception. In order to achieve this ultimate goal it will be necessary to determine the relationships among the physical parameters of the stimulus, the underlying physiological mechanisms and the anatomical organization, linking these factors to psychophysical results and behavioral observations. In the short-term, the duration of the proposed research, we will perform anatomical investigations on the hairless (glabrous) skin of mammals which will test four specific hypotheses regarding the sense of touch and lay a basis for future, additional models for taction. We will test whether: a) there are four distinct populations of tactile receptors within the glabrous skin of humans and cat, but only three such populations in the monkey; b) Ruffini endings, as seen in hairy skin, constitute one of the classes of mechanoreceptors found within the glabrous skin of mammals; c) tactile receptors within the glabrous skin lie in an ordered array, and d) the loss of tactile sensitivity that occurs during the normal aging process may be explained by a change in the receptor distribution within the glabrous skin. These four hypotheses will be tested by determining the distribution and organization of the tactile receptors using established histological techniques on cutaneous tissue obtained from the glabrous skin regions (specifically the fingertips and the thenar eminence) of human cadavers of various ages and monkeys, and from the footpads of cats.