Responses of Neurons in Cat Primary Auditory Cortex to Bird Chirps: Effects of Temporal and Spectral Context

Abstract

The responses of neurons to natural sounds and simplified natural sounds were recorded in the primary auditory cortex (AI) of halothane-anesthetized cats. Bird chirps were used as the base natural stimuli. They were first presented within the original acoustic context (at least 250 msec of sounds before and after each chirp). The first simplification step consisted of extracting a short segment containing just the chirp from the longer segment. For the second step, the chirp was cleaned of its accompanying background noise. Finally, each chirp was replaced by an artificial version that had approximately the same frequency trajectory but with constant amplitude. Neurons had a wide range of different response patterns to these stimuli, and many neurons had late response components in addition, or instead of, their onset responses. In general, every simplification step had a substantial influence on the responses. Neither the extracted chirp nor the clean chirp evoked a similar response to the chirp presented within its acoustic context. The extracted chirp evoked different responses than its clean version. The artificial chirps evoked stronger responses with a shorter latency than the corresponding clean chirp because of envelope differences. These results illustrate the sensitivity of neurons in AI to small perturbations of their acoustic input. In particular, they pose a challenge to models based on linear summation of energy within a spectrotemporal receptive field.

Auditory abstraction from spectro-temporal features to coding auditory entities

“…However, the responses of the neurons studied here, although recorded in anesthetized cats, are often tonic (8) and have rich temporal structure ( Fig. 5 and ref.…”

“…All recordings were performed in halothane-anesthetized cats by using a single set of stimuli consisting of natural and modified bird vocalizations (8)(9)(10). To investigate changes in stimulus representations across processing stations, it is necessary to use stimuli that are rich enough to engage processing mechanisms at all levels of the auditory pathway.…”

“…4 for examples of these variants for one bird chirp. A detailed description of the stimuli is provided in (8). We studied how neurons in the same three stations cooperate to code these sounds (11).…”

“…In addition, MI was estimated by using the distribution of binary words (43,44). To this end, each spike train was discretized in several temporal resolutions (1,2,4,8,16, and 32 ms, yielding 3-120 bins per stimulus), and the resolution and temporal window that yielded maximal (bias corrected) MI were selected.…”

Representation of Sounds in Auditory Cortex of Awake Rats (Dissertation)

“…Since the early start of single-unit recordings in the auditory system (Davies et al, 1956;Galambos and Davis, 1943) many acoustic stimuli have been used to probe neurons in auditory cortex, including tones (Moshitch et al, 2006), sweeps (Orduña et al, 2001;Zhang et al, 2003), ripples (Kowalski et al, 1996a,b), TORCS (Elhilali et al, 2004) and natural sounds (Bar-Yosef et al, 2002;Machens et al, 2004). However, no acoustic feature analogous to the oriented bar has emerged (Nelken, 2004;Nelken et al, 2003).…”