Abstract #21995, Date "Monday, Feb 5 2001 1:00PM - 12:00PM " Session "L17 Auditory Pathways, Cortex III "

Plasticity of spectrotemporal coding in primary auditory cortex enabled by cholinergic modulation

Raluca MOUCHA , Pritesh PANDYA , Jessica Lynn VAZQUEZ , Navzer D. ENGINEER , Daniel RATHBUN , Michael Paul KILGARD

"Cholinergic modulation enables activation of plasticity mechanisms involved in creating precise representations of relevant stimulus features. This type of plasticity has been shown to be highly specific to the experienced stimulus, and parallels plasticity that results from natural learning. We used nucleus basalis (NB) stimulation to explore the principles of cortical reorganization as they apply to the representation of complex dynamic stimuli such as frequency modulated (FM) sweeps, in rat auditory cortex. We paired five downward FM sweeps (160ms duration, 6.25oct/s), each spanning a different octave (2-1KHz, 4-2KHz, 8-4KHz, 16-8KHz, 32-16KHz) with NB stimulation 200-300 times per day for 20 days, under two different conditions. One group (n=3) heard only the paired stimuli (CS+ condition), while a second group (n=3) heard paired and unpaired FM sweeps of different rates and direction, randomly interleaved (CS+ with CS- condition). Dense microelectrode mapping techniques were used to quantify the response properties of auditory cortical neurons. Multiunit data was collected from 50-70 penetrations in each animal. For the CS+ with CS-condition we observed significant effects on frequency selectivity (up to 15% increase in BW20), decrease in intensity thresholds by 4dB(p<0.01), and response latency decrease (from 18ms to 16ms, p<0.01) . Plasticity induced with CS+ only pairing, did not reach significance. These results suggest that providing a contrast (or context) for learning, has the potential to alter cortical responses to better represent the statistics of the input learned. "