title: Cortical and thalamic connectivity of the auditory anterior ectosylvian cortex of early-deaf cats: Implications for neural mechanisms of crossmodal plasticity.
abstract: Early hearing loss leads to crossmodal plasticity in regions of the cerebrum that are dominated by acoustical processing in hearing subjects. Until recently, little has been known of the connectional basis of this phenomenon. One region whose crossmodal properties are well-established is the auditory field of the anterior ectosylvian sulcus (FAES) in the cat, where neurons are normally responsive to acoustic stimulation and its deactivation leads to the behavioral loss of accurate orienting toward auditory stimuli. However, in early-deaf cats, visual responsiveness predominates in the FAES and its deactivation blocks accurate orienting behavior toward visual stimuli. For such crossmodal reorganization to occur, it has been presumed that novel inputs or increased projections from non-auditory cortical areas must be generated, or that existing non-auditory connections were 'unmasked.' These possibilities were tested using tracer injections into the FAES of adult cats deafened early in life (and hearing controls), followed by light microscopy to localize retrogradely labeled neurons. Surprisingly, the distribution of cortical and thalamic afferents to the FAES was very similar among early-deaf and hearing animals. No new visual projection sources were identified and visual cortical connections to the FAES were comparable in projection proportions. These results support an alternate theory for the connectional basis for cross-modal plasticity that involves enhanced local branching of existing projection terminals that originate in non-auditory as well as auditory cortices.
authors.affiliation: Virginia Commonwealth University School of Medicine, Department of Anatomy and Neurobiology, Richmond, VA 23298, USA. Electronic address: mameredi@vcu.edu.
authors.forename: M Alex
authors.initials: MA
authors.lastname: Meredith
authors.affiliation: Virginia Commonwealth University School of Medicine, Department of Anatomy and Neurobiology, Richmond, VA 23298, USA.
authors.forename: H Ruth
authors.initials: HR
authors.lastname: Clemo
authors.affiliation: Virginia Commonwealth University School of Medicine, Department of Anatomy and Neurobiology, Richmond, VA 23298, USA; University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Corley
authors.affiliation: Cerebral Systems Laboratory, The Brain and Mind Institute, Natural Sciences Centre, University of Western Ontario, London, Ontario N6A 5B7, Canada.
authors.forename: Nicole
authors.initials: N
authors.lastname: Chabot
authors.affiliation: Cerebral Systems Laboratory, The Brain and Mind Institute, Natural Sciences Centre, University of Western Ontario, London, Ontario N6A 5B7, Canada.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Lomber
mesh_terms: D000161:Acoustic Stimulation; D000222:Adaptation, Physiological; D000367:Age Factors; D000818:Animals; D001303:Auditory Cortex / Q000254:growth & development / Q000503:physiopathology*; D001306:Auditory Pathways / Q000503:physiopathology; D001307:Auditory Perception; D002415:Cats; D004195:Disease Models, Animal; D006309:Hearing; D034381:Hearing Loss / Q000139:chemically induced / Q000503:physiopathology* / Q000523:psychology; D007612:Kanamycin; D056347:Neuroanatomical Tract-Tracing Techniques; D009473:Neuronal Plasticity; D010775:Photic Stimulation; D013788:Thalamus / Q000254:growth & development / Q000503:physiopathology*; D014793:Visual Cortex / Q000254:growth & development / Q000503:physiopathology*; D014796:Visual Perception
chemical_list: D007612:Kanamycin
keywords: Hearing loss; Sensory substitution; Somatosensory cortex; Thalamus; Visual cortex