Sensory Neuroscience
Our perceptual capacities depend upon information transmitted from nerves within the skin, the eyes, the ears and other sense organs to higher centres of the brain. This information is conveyed in the form of small electrical impulses which, in our experiments, are recorded from individual nerve cells by inserting microelectrodes into the brain in order to investigate the processing of sensory information that arises from tactile receptors in the skin. The purpose is to identify the brain regions involved in processing tactile information and to reveal the ways in which that information is coded in the impulse patterns of brain cells.
Current Projects
Neural mechanisms in tactile kinaesthetic and pain sensation
Organization and Function of the Sensory Cortex
| Sensory information for touch and for our sense of body position (kinaesthesia) is conveyed to two or more processing areas in the cerebral cortex, known as somatosensory areas I and II (SI and SII). Our experiments have established that these two areas are organized in parallel neural networks for sensory processing, and that this organizational scheme (A, in Figure 1) applies in primates as well as non-primate mammals, in contrast to some earlier claims for a serial scheme in primates (B in Figure 1). | 
Figure 1. Parallel (A) and Serial (B) systems of organization for thalamo-cortical processing of tactile information.
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Transmission Characteristics at synaptic relays in tactile and kinaesthetic sensory pathways
When sensory systems are activated, the signals arising in the receptors must be conveyed through a series of relay nuclei before reaching the sensory areas of cortex. These signals arise from several different classes of sensory receptors and sensory nerves in skin, muscles and joints and convey information about different features of sensory stimuli. We have developed an analytical approach to quantify the transmission characteristics for these different classes of sensory nerve fibres, this is based on a paired electrophysiological recording (Fig.2) in which recordings are made from individual sensory fibres in very fine peripheral nerve strands that remain in continuity with the central nervous system. At the same time, a microelectrode is used to record from the central target neurone whose input is derived from the peripheral sensory fibre under study. In this way we can quantify the security of the synaptic linkages formed in the brain by the different classes of sensory nerves (Fig.3) and to examine the likely contribution to sensory and perceptual experience.
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Figure 2. Experimental arrangement showing the recording sites within the DCN and on the hind-limb interosseous nerve proximal to the custer of PC receptors (PCs).
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Figure 3. Single sensory nerve impulses in PC fibres of the interosseous nerve (i.m.) evoke spike output from DCN target neurones. Traces show paired recordings from a DCN neurone and a PC sensory fibre of the interossous nerve with direct evidence for the high security of the linkage of this sensory relay. the lowest traces show the wave form of a 200Hz vibration.
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The role of parallel ascending sensory systems in tactile sensation
Information from tactile receptors and sensory nerves supplying the skin projects through the spinal cord and lower brain over two or three major pathways that are organized as parallel ascending sensory systems. One of our projects is concerned with a quantitative comparative evaluation of the capacity of each of these pathways to contribute to tactile sensory experience. Many of our earlier studies have characterized the capacity of the neural pathway projecting through the Dorsal Column Nuclei (and its component Cuneate and Gracile Nuclei). However, our current research is directed to an analysis of the capacity of the spino-cervical and other ascending spinal pathways to contribute to tactile discriminative abilities. This will enable us to define their role vis-à-vis the role of the Dorsal Column system.
Psychophysical Studies in Tactile Sensation
Psychophysical experiments are also being conducted to evaluate tactile sensory capacities in human subjects to establish correlations between subjective sensory capacities and the neural interactions and coding properties observed in microelectrode studies.
The Capacity of the Brain to Adapt to Injury
Although the brain and spinal cord nerve tracts are unable to regenerate following injury there have been numerous reports in recent years that the brain and spinal cord have the capacity to undergo functional or structural re-organization, or plasticity, as it is called, in response to experimentally-induced nerve injury. We have used electrophysiological recordings within the somatosensory system to investigate the extent to which such reorganization may occur in response to nerve injury.
Staff
Dr David Mahns, NHMRC Research Officer
Dr Vineet Sahai, PhD Student
Ms Christine Riordan, Senior Technical Officer
Grants and Awards
Continuing support from the National Health and Medical Research Council (NHMRC) of Australia and the Australian Research Council (ARC) over many years.
Recipient of Australasian Science Prize in 2003
Some Recent Publications
Mahns, D.A., Coleman, G.T., K.W.S. Ashwell &
Rowe, M.J. (2003). Tactile sensory function in the forearm of the Monotreme Tachyglossus aculeatus.
Journal of Comparative Neurology, 459, 173-185.
Coleman, G.T. Zhang, H.Q. &
Rowe, M.J. (2003). Transmission security for single kinesthetic afferent fibers of joint origin and their target cuneate neurons in the cat.
Journal of Neuroscience, 23, 2980-2992.
Coleman, G.T.,
Mahns, D.A., Zhang, H.Q. &
Rowe, M.J. (2003). Impulse propagation over tactile and kinaesthetic sensory axons to central target neurons of the cuneate nucleus in the cat.
Journal of Physiology, 550, 553-562.
Rowe, M.J.,
Mahns, D., Bohringer, R.C., Ashwell, K.W.S. &
Sahai, V. (2003). Tactile neural mechanisms in monotremes.
Comparative Biochemistry and Physiology, 136, 883-893.
Rowe, M.J.,
Mahns, D.A. &
Sahai, V. (2004). The capacity of tactile systems for the detection and discrimination of sensory events. In: Touch, Blindness and Neuroscience, Eds. Ballesteros, S. & Heller, M., UNED, Madrid, p.221-234. (ISBN:84-362-4887-2).
Rowe, M.J.,
Mahns, D.A. &
Sahai, V. (2004). Monotreme tactile mechanisms: from sensory nerves to cerebral cortex.
Proceedings of the Linnean Society of N.S.W., 125, 301-317.
Rowe, M.J. (2004).
Multiple representation of sensory system input in the cerebral cortex: the new phrenology?
Neuroscience Letters, 361, 98-101.
Rowe, M.J. (2004). Our tactile brain.
Australasian Science, 25, 14-17.
Rowe, M.J., Tracey, D.J., Ivanusic, J.J.,
Mahns, D.A. &
Sahai, V. (2005). Mechanosensory perception: are there contributions from bone-associated receptors?
Clinical and Experimental Pharmacology and Physiology, 32, 100-108.