et al. 1998). However, the later study only examined acquisition rates, not
retention, and used a small stimulus set. Thus, it remains to be seen whether
general auditory effects are observable in male songbirds, where the AFP
shows clear selectivity to BOS (Doupe 1997).
Volumetric studies are consistent with the lesion work in suggesting a
role for the AFP in song perception, particularly among females. In adult
female brown-headed cowbirds, the volume and number of neurons in
lMAN is positively correlated with the bird’s ability to discriminate among
male songs (Hamilton et al. 1997). In addition, preliminary evidence suggests that female lMAN volume may also correlate positively with male
song repertoire size among several species of European warblers (DeVoogd
et al. 1996).
2.3.3.4. Behavioral-State Modulation of Auditory Responses
A role for the AFP in song perception does not exclude a role for the VMP
in song perception. Some controversy remains as to whether the VMP
contributes to song perception. Throughout the song system, auditory
responses of neurons are strongly modulated by behavioral state (Dave
et al. 1998a; Schmidt and Konishi 1998). Surprisingly, the modulation of
response is such that activity is suppressed in awake birds relative to sleeping birds. One report that systematically studied behavioral state changes
found virtually no auditory activity in RA in awake birds but strong auditory responses in sleeping birds (Dave et al. 1998a). (Subsequent single-unit
studies have suggested that the sleep state may be involved in song playback, perhaps associated with motor program consolidation; see Dave and
Margoliash 2000.) Another study, which focused on the contribution of HVc
and lMAN to RA auditory responses in anesthetized birds, reported (in a
small part of the overall design) RA auditory responses in awake birds
(Vicario and Yohay 1993). It is difficult to resolve these apparently conflicting observations. The Dave, Yu, and Margoliash (1998a) study used
chronic recording techniques, and male birds were sufficiently unhindered
that they freely sang in response to females. The auditory stimuli were presented after the females were removed from cages adjacent to those of the
subjects. The Vicario and Yohay (1993) study used restrained animals in a
sound-attenuation chamber and did not directly observe the animals during
acoustic stimulation. It is difficult to assess whether these differences in
design could result in sufficient differences in behavioral state to explain
the variation in RA auditory responsiveness. A recent lesion study of RA
also claimed to show an effect on conspecific song recognition (Vicario
et al. 2001). The behavioral effects were small, however, and whether the
locus of the effects of the lesions was within RA remains unresolved.
The failure to find auditory responses in the VMP in awake birds is a
strong challenge to the theory that the VMP is involved in song perception
350
T.Q. Gentner and D. Margoliash
retention, and used a small stimulus set. Thus, it remains to be seen whether
general auditory effects are observable in male songbirds, where the AFP
shows clear selectivity to BOS (Doupe 1997).
Volumetric studies are consistent with the lesion work in suggesting a
role for the AFP in song perception, particularly among females. In adult
female brown-headed cowbirds, the volume and number of neurons in
lMAN is positively correlated with the bird’s ability to discriminate among
male songs (Hamilton et al. 1997). In addition, preliminary evidence suggests that female lMAN volume may also correlate positively with male
song repertoire size among several species of European warblers (DeVoogd
et al. 1996).
2.3.3.4. Behavioral-State Modulation of Auditory Responses
A role for the AFP in song perception does not exclude a role for the VMP
in song perception. Some controversy remains as to whether the VMP
contributes to song perception. Throughout the song system, auditory
responses of neurons are strongly modulated by behavioral state (Dave
et al. 1998a; Schmidt and Konishi 1998). Surprisingly, the modulation of
response is such that activity is suppressed in awake birds relative to sleeping birds. One report that systematically studied behavioral state changes
found virtually no auditory activity in RA in awake birds but strong auditory responses in sleeping birds (Dave et al. 1998a). (Subsequent single-unit
studies have suggested that the sleep state may be involved in song playback, perhaps associated with motor program consolidation; see Dave and
Margoliash 2000.) Another study, which focused on the contribution of HVc
and lMAN to RA auditory responses in anesthetized birds, reported (in a
small part of the overall design) RA auditory responses in awake birds
(Vicario and Yohay 1993). It is difficult to resolve these apparently conflicting observations. The Dave, Yu, and Margoliash (1998a) study used
chronic recording techniques, and male birds were sufficiently unhindered
that they freely sang in response to females. The auditory stimuli were presented after the females were removed from cages adjacent to those of the
subjects. The Vicario and Yohay (1993) study used restrained animals in a
sound-attenuation chamber and did not directly observe the animals during
acoustic stimulation. It is difficult to assess whether these differences in
design could result in sufficient differences in behavioral state to explain
the variation in RA auditory responsiveness. A recent lesion study of RA
also claimed to show an effect on conspecific song recognition (Vicario
et al. 2001). The behavioral effects were small, however, and whether the
locus of the effects of the lesions was within RA remains unresolved.
The failure to find auditory responses in the VMP in awake birds is a
strong challenge to the theory that the VMP is involved in song perception
350
T.Q. Gentner and D. Margoliash