Current Research

 

 

                                     

 

 

 

My research career began in the Departments of Anatomy&Neurobiology and Physical Therapy at Virginia Commonwealth University in Richmond, Virginia

 

My dissertation:

 

Cross-Modal Circuitry within the Anterior Ectosylvian Cortex of the Cat: Anatomical and Functional Connections from Auditory Field AES to Somatosensory SIV.

 

Abstract:

 Events processed by one sensory modality can influence the perception or detection of those in another, but the neural circuitry underlying these multisensory phenomena is largely unknown. Representations of different sensory modalities in the cerebral cortex sometimes reside in physical proximity to one another, a relationship that may promote cross-modal connections. This possibility was explored in the banks of the anterior ectosylvian sulcus (AES) of the cat cortex, where somatosensory (SIV) and auditory (FAES) representations share a common border.  In 4 cats, neuroanatomical tracer injected into SIV retrogradely labeled pyramidal-type neurons in laminae III (81%) and V (19%) in FAES.  In another 5 cats, tracer deposits placed within FAES orthogradely labeled axon terminals in the supra- (79%) and infragranular (19%) layers of SIV. This pattern of connectivity is representative of a feedback cortico-cortical projection.

The functional properties of the cross-modal projection from FAES to SIV were examined in 9 chronically prepared, anesthetized cats.  Extracellular recordings were made from 104 SIV neurons in response to electrical stimulation of FAES but orthodromic activation was not observed in any SIV neuron.  Of the 69 SIV neurons tested to determine if their responses to tactile stimulation were modified by concurrent electrical stimulation of the FAES, 47 (68%) showed a significant reduction in response, while only 4 (6%) showed an increased discharge. This FAES-induced suppression of SIV activity was blocked by the application of the GABA-A antagonist, bicuculline methiodide (100µM).  Tests involving the adjacent areas auditory AI or somatosensory SV yielded no SIV response changes and antidromic stimulation techniques revealed that FAES neurons (80%, 4/5) projecting to SIV carried auditory signals. 

The lack of orthodromic input from FAES to SIV, the effect of FAES stimulation on SIV responses, and the sensitivity of the effect to bicuculline are consistent with the idea that the functional connection between the two regions results in suppression.  Ultimately, these observations demonstrate that representations of the different sensory modalities within the AES cortex are connected and that the suppressive multisensory interactions mediated by this neuronal circuit result from a heretofore undescribed form of excitatory-inhibitory multisensory convergence.

 

       I am currently continuing my collaboration with my graduate advisor Dr. Alex Meredith:

We use neurophysiological, anatomical, and immunocytochemical techniques to examine the circuitry underlying cortical processing of simultaneous information from different sensory modalities, and how the loss or injury to one sensory system might lead to compensatory changes in the others. Current research focuses on the architecture of, and role of inhibition in, multisensory circuits of the cerebral cortex. Future efforts will be directed toward examining the role of these circuits in the plasticity of sensory representations following early (i.e., congenital) and late (i.e., acquired after maturity) sensory loss.

 

 

Suggested readings:

 

Dehner, L.R.  Cross-Modal Circuitry within the Anterior Ectosylvian Cortex of the Cat:  Anatomical and Functional Connections from Auditory Field AES to Somatosensory SIV. (Doctoral dissertation, Virginia Commonwealth University, 2000) ISBN 0-599-81884-0.

 

Dehner, L.R., Keniston, L.P., Clemo, H.R., and M.A. Meredith. (2004)  Cross –modal Circuitry Between Auditory and Somatosensory Aread of the Cat Anterior Ectosylvian Sulcal Cortex:  A ‘New’ Inhibitory Form of Multisensory Convergence Cerebral Cortex 14(4): 387-403.

 

Meredith, M.A., Clemo, H.R. and L.R. Dehner. (2000)

Effects of innocuous and noxious somatosensory stimulation on neurons in the ferret superior colliculus. Somatosensory and Motor Research 17 (4) 297-308.

 

Stein, B.E. and M.A. Meredith. The Merging of the Senses (1993) Cambridge: MIT press.

 

Wallace, M.T., Meredith, M.A., and B.E. Stein: The integration of multiple sensory inputs in cat cortex. Experimental Brain Research. 91:484-488, 1992.

 

Pub Med