ENVIRONMENTAL ENRICHMENT INCREASES RESPONSE STRENGTH AND PAIRED-PULSE DEPRESSION OF AUDITORY CORTEX NEURONS by CHERIE R. PERCACCIO, M.S, M.S. DISSERTATION Presented to the Faculty of The University of Texas at Dallas in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY IN COGNITION AND NEUROSCIENCE THE UNIVERSITY OF TEXAS AT DALLAS May, 2006