Dissecting natural sensory plasticity: hormones and experience in a maternal context

Abstract

There is a growing consensus that the auditory system is dynamic in its representation of behaviorally relevant sounds. The auditory cortex in particular seems to be an important locus for plasticity that may reflect the memory of such sounds, or functionally improve their processing. The mechanisms that underlie these changes may be either intrinsic because they depend on the receiver's physiological state, or extrinsic because they arise from the context in which behavioral relevance is gained. Research in a mouse model of acoustic communication between offspring and adult females offers the opportunity to explore both of these contributions to auditory cortical plasticity in a natural context. Recent works have found that after the vocalizations of infant mice become behaviorally relevant to mothers, auditory cortical activity is significantly changed in a way that may improve their processing. Here we consider the hypothesis that maternal hormones (intrinsic factor) and sensory experience (extrinsic factor) contribute together to drive these changes, focusing specifically on the evidence that well-known experience-dependent mechanisms of cortical plasticity can be modulated by hormones.

Fig. 1

Sample spectrograms of two bouts of natural ultrasonic calls emitted by postnatal day 7 pups. Note the rhythmic nature of the calls, which are typically separated by ~180–200 ms (onset to onset).

Fig. 2

Schematic representation of estradiol and progesterone profiles during pregnancy and lactation in the mouse (Atkinson and Leathem, 1946; Barkley et al., 1979; Bell and Dawson, 1983; Critser et al., 1982; McCormack and Greenwald, 1974). The vertical dashed line denotes the time of parturition. The grey shaded area encompasses the period in which pups produce ultrasonic vocalizations (Elwood and Keeling, 1982; Graham and Letz, 1979; Pontet et al., 1989; Vieira and Brown, 2002).

Fig. 3

Neuroanatomical model for information flow leading to maternal behavior. Numbers denote components that are referred to in the text. Hormones can act at the numbered levels (1–4).