Development of song responses in the zebra finch caudomedial neostriatum: Role of genomic and electrophysiological activities

Abstract

Zebra finches first form demonstrable memories of specific songs between 25 and 35 days of age--several days after fledging from the nest. What accounts for the late onset of specific song memory formation? Here we investigated physiological development of the caudomedial neostriatum (NCM), part of the avian analogue of auditory cortex and a probable component of the system involved in song perception. Two types of physiological responses were characterized: electrophysiological (single-unit spike rate) and genomic (induction of the immediate early gene zenk, also known as zif-268, egr-1, ngfi-a, krox-24). We found that by day 20, zebra finches already have robust electrophysiological responses in NCM to song stimulation. Spike activity was greater in response to conspecific songs compared to heterospecific songs, white noise, or tones, and approximately 10% of the units showed selective responses to forward versus reversed songs. In contrast, at this age the zenk gene is expressed at a constitutively high level and undergoes no further induction in response to song presentation. At day 30, electrophysiological responses remained similar, but the zenk gene began to shift from a constitutive to an inducible pattern of expression. These results are consistent with a general role for NCM in the representation of song auditory patterns, and with a role for zenk gene expression in governing the efficiency of specific song memory storage at different ages.

Hemispheric differences in processing of vocalizations depend on early experience

“…It has been shown that the avian NCM, a cortical-like auditory area in the caudal telencephalon, responds selectively to conspecific songs both in adults and juveniles (12)(13)(14)32). In addition, from experiments in adults, we know that NCM neurons encode auditory memories of the songs of individual conspecifics, which differ due to learning (14).…”

An Analysis of the Neural Representation of Birdsong Memory

“…According to Stripling et al (2001), in the study by Bolhuis et al (2000), IEG expression was measured "far more laterally than in any other study of the ZENK response in zebra finches" (p. 178).…”

“…There has been some debate concerning the lateral extent of the NCM (Stripling et al, 2001). In the present study, we com-pared IEG expression in two locations within the NCM: medial [at a location comparable with previous studies (Table 1)] and lateral (comparable with the location sampled by Bolhuis et al, 2000).…”

Birdsong: From behaviour to brain

“…However, at day 30 the ZENK mRNA begins to shift from a constitutive to an inducible pattern of expression. These observations suggest that longterm auditory memories are stored in NCM, or that the IEG-mediated neural plasticity resulting from song playback is directed towards the projections of NCM (Jin & Clayton 1997;Stripling et al 2001;Bailey & Wade 2003). In the female and male context, increased expression was seen in the auditory forebrain below HVC (fields L1 and L3, caudal HV), regions known to show ZENK induction due to hearing song independent of singing (Jarvis & Nottebohm 1997).…”