(see Margoliash 1997). A related question is whether any song-system
neurons exhibit auditory activity during the day. One study recording multiunit activity identified an apparent loss of auditory activity in male zebra
finch HVc during daytime recordings (Schmidt and Konishi 1998). In
contrast, several other studies identified daytime auditory activity in HVc
of canaries, white-crowned sparrows, and zebra finches (McCasland and
Konishi 1981; Margoliash 1986; Yu and Margoliash 1996). A study of single
HVc neurons concluded that many neurons retain auditory responsiveness
during the day, albeit at consistently lower levels than observed at night.
Consistent if weak auditory responses were also observed in area X in
daytime recordings (Rauske and Margoliash 1999), and daytime auditory
responses in nonsinging birds have also been reported for lMAN recordings (Hessler and Doupe 1999). This suggests that the AFP but not the VMP
retains auditory activity during the day. If this conclusion is established, and
these results are obtained in other species and under other behavioral
measures of perceptual responses, they would provide strong evidence
against the motor theory hypothesis of perception and strong evidence for
the ontogenetic-coupling hypothesis.
2.3.4. Plasticity and Functional Constraints
The ethologically relevant functions of any representational system derive
from a combination of an organism’s evolutionary history and ontogenetic
experience. Both of these processes can lead to plasticity in the neural
system and thus can constrain the form of a representation at any given
point in time. Plasticity can result from time-dependent components of
ontogeny and from experience-dependent components (i.e., learning). The
combination of these two components gives rise to the so-called “critical
period” in development where certain experiences must occur at specific
times in order for representations to develop normally (for discussions of
critical periods, see Bateson 1979). Even after a normal sensory development, representational plasticity can be induced by altering experience in
the periphery (e.g., by peripheral denervation, stimulus restriction, or
illusion; Pons et al. 1991; Recanzone 1998) or by central lesions (Nudo et
al. 1996). These effects have been observed in many sensory modalities, and
although usually examined in relation to cortical representations (e.g., Jones
2000), they have also been observed in more peripheral structures (Gao and
Suga 1998; Gold and Knudsen 2000). Moreover, representational plasticity
is observed not only in response to abnormal experience. Simply training a
monkey to perform a frequency-discrimination task increases the cortical
representation (number of cells), sharpness of tuning, and response latency
for the behaviorally relevant frequencies (Recanzone et al. 1993). Likewise,
in humans and bats, tonotopic responses in the auditory cortex can be
modulated by simple conditioning procedures (Morris et al. 1998; Gao and
7. Neuroethology of Vocal Communication
351
neurons exhibit auditory activity during the day. One study recording multiunit activity identified an apparent loss of auditory activity in male zebra
finch HVc during daytime recordings (Schmidt and Konishi 1998). In
contrast, several other studies identified daytime auditory activity in HVc
of canaries, white-crowned sparrows, and zebra finches (McCasland and
Konishi 1981; Margoliash 1986; Yu and Margoliash 1996). A study of single
HVc neurons concluded that many neurons retain auditory responsiveness
during the day, albeit at consistently lower levels than observed at night.
Consistent if weak auditory responses were also observed in area X in
daytime recordings (Rauske and Margoliash 1999), and daytime auditory
responses in nonsinging birds have also been reported for lMAN recordings (Hessler and Doupe 1999). This suggests that the AFP but not the VMP
retains auditory activity during the day. If this conclusion is established, and
these results are obtained in other species and under other behavioral
measures of perceptual responses, they would provide strong evidence
against the motor theory hypothesis of perception and strong evidence for
the ontogenetic-coupling hypothesis.
2.3.4. Plasticity and Functional Constraints
The ethologically relevant functions of any representational system derive
from a combination of an organism’s evolutionary history and ontogenetic
experience. Both of these processes can lead to plasticity in the neural
system and thus can constrain the form of a representation at any given
point in time. Plasticity can result from time-dependent components of
ontogeny and from experience-dependent components (i.e., learning). The
combination of these two components gives rise to the so-called “critical
period” in development where certain experiences must occur at specific
times in order for representations to develop normally (for discussions of
critical periods, see Bateson 1979). Even after a normal sensory development, representational plasticity can be induced by altering experience in
the periphery (e.g., by peripheral denervation, stimulus restriction, or
illusion; Pons et al. 1991; Recanzone 1998) or by central lesions (Nudo et
al. 1996). These effects have been observed in many sensory modalities, and
although usually examined in relation to cortical representations (e.g., Jones
2000), they have also been observed in more peripheral structures (Gao and
Suga 1998; Gold and Knudsen 2000). Moreover, representational plasticity
is observed not only in response to abnormal experience. Simply training a
monkey to perform a frequency-discrimination task increases the cortical
representation (number of cells), sharpness of tuning, and response latency
for the behaviorally relevant frequencies (Recanzone et al. 1993). Likewise,
in humans and bats, tonotopic responses in the auditory cortex can be
modulated by simple conditioning procedures (Morris et al. 1998; Gao and
7. Neuroethology of Vocal Communication
351