Responses to linear and logarithmic frequency‐modulated sweeps in ferret primary auditory cortex

Abstract

Multi-unit responses to frequency-modulated (FM) sweeps were studied in the primary auditory cortex of ferrets using six different stimulation paradigms. In particular, the differences between the responses to linear FM sweeps (where frequency changes linearly with time) and logarithmic FM sweeps (where frequency changes exponentially with time) were emphasized. Some general features of the responses to FM sweeps are independent of the exact details of the frequency trajectory. Both for linear and for logarithmic FM sweeps, a short burst of spikes occurred when the sweep reached a triggering frequency close to the best frequency of the cluster. The neuronal preference for FM velocity was also independent of frequency trajectory. Thus, clusters that responded best to slow logarithmic FM also preferred slow linear FM and vice versa. Consequently, topographic distributions of velocity preference were roughly independent of the stimulation paradigm. Other characteristics of the responses, however, depended on the exact details of the frequency trajectory. A significant number of clusters showed large differences in directional sensitivity between linear and logarithmic FM sweeps; these differences depended on the velocity preference of the clusters in some paradigms but not in others. Consequently, topographic distributions of directional sensitivity differed between linear and logarithmic paradigms. In conclusion, some characteristics of cluster responses to FM sweeps depend on the exact details of the stimulation paradigm and are not 'invariants' of the cluster.

Detection of spatial cues in linear and logarithmic frequency-modulated sweeps

“…The experiment was run in a block design in which the sweep's duration, direction (up or down in frequency), and type (linear or log) were held constant within a run. Each subject comneurophysiological studies (Brimijoin & O'Neill, 2005;Fuzessery, Richardson, & Coburn, 2006;Mendelson & Grasse, 1992;Mendelson, Schreiner, Sutter, & Grasse, 1993;Nelken & Versnel, 2000;Razak & Fuzessery, 2006, human developmental research (Colombo & Horowitz, 1986), studies of tonal languages (Luo, Boemio, Gordon, & Poeppel, 2007), and studies of music perception (d 'Alessandro, Rosset, & Rossi, 1998), in no prior study has the spatial sensitivity of the auditory system to these sounds been investigated. 1 The second goal of this study was to investigate theoretical issues related to the localization of high-frequency complex sounds.…”

“…We used both an up and a down sweep because previous work has suggested the existence of neurons selective to sweep direction (Mendelson & Cynader, 1985;Mendelson & Grasse, 1992;Nelken & Versnel, 2000). We investigated binaural sensitivity to both linear and logarithmic sweeps because envelope fluctuations at the outputs of auditory filters will have different rise/decay slopes, depending on sweep type, and because most previous work in this area has included only linear sweeps in spite of the logarithmically organized peripheral and cortical tonotopy (Clopton, Winfield, & Flammino, 1974;M.…”

Coding of FM sweep trains and twitter calls in area CM of marmoset auditory cortex

“…The first is a period of suppression after the onset response, which is followed by a rebound from suppression in a subsequent cycle (Aitkin et al, 1968;Creutzfeldt et al, 1980;Fitzpatrick et al, 1999;Lu et al, 2000;Nelken et al, 2000). This is most important for repetitive sounds with a total duration that overlaps the rebound period.…”

Background sounds contribute to spectrotemporal plasticity in primary auditory cortex

“…Some discrepancies could be explained by the difference in the way that FM sweeps are generated. For example, direction selectivity maps differ between linear and logarithmic FMs (Nelken and Versnel 2000), and between continuous (Shamma et al 1993) and separate sweeps (Heil et al 1992;Mendelson et al 1993). Thus it appears that FM direction selectivity depends strongly on the paradigm used to measure it.…”