LONG-TERM AND SHORT-TERM PLASTICITY INDUCED BY EXPERIENCE WITH SPECTROTEMPORALLY COMPLEX SOUNDS IN RAT AUDITORY CORTEX by

Processing of short frequency modulated (FM) sweeps has not been extensively studied in the central auditory system. Here we report the neural representations of oneoctave FM sounds along three centers of the auditory pathway: thalamus, primary auditory cortex (A1) and posterior auditory field (PAF). Dense microelectrode mapping techniques were used to collect multiunit responses from 249 sites in five barbiturate anesthetized rats. Nearly all sites had a strong onset response to these sounds and some had a 2nd excitatory peak (mostly in PAF) or oscillatory patterns (mostly in thalamus). Response strength in thalamus was more than two fold greater than the two cortical fields. Response latency increased along the ascending pathway, consistent with serial processing of auditory inputs. Responses to one-octave FM’s were influenced by RF differences. PAF sites had wider bandwidths, while A1 and thalamus sites typically had asymmetric tuning skewed towards low frequencies. Direction selectivity systematically decreased with each station above thalamus. Onset responses were strongest for fast rates when FM sweeps moved toward the center of the receptive field, and non-rate selective for FM’s that started near the center. Additional late action potentials were evoked in A1 in response to long duration (slow) FM’s, but not in thalamus or PAF. These results indicate that receptive field properties strongly influence the central representation of short FM sounds.