Margoliash 1992). The field L complex is the primary telencephalic target
for auditory information arriving via several parallel pathways from the Ov
complex in the thalamus (Fig. 7.3). Neurons in the shell of Ov also project
to the caudomedial portion of the neostriatum (NCM) (Durand et al. 1992;
Vates et al. 1996). The subregions of field L are densely interconnected and
project to the NCM and reciprocally to the lateral portion of the caudal
ventral hyperstriatum (clHV). The NCM and clHV share reciprocal connections with the caudal medial portion of HV (cmHV). Figure 7.3 provides
a schematic for this complicated pattern in songbirds.
Neurons in clHV, L1, and L3 also project to the neostriatum immediately
ventral to HVc, referred to as the “shelf” (Kelley and Nottebohm 1979).
Neurons in the shelf are auditory (Scheich et al. 1979a; Müller and
Leppelsack 1985), and it has been proposed that the shelf is a source of
auditory input to HVc. The projections of the shelf into HVc are extremely
sparse, however (L. Katz, cited in Margoliash 1987; Vates et al. 1996). One
proposition is that dendrites in caudal HVc, which extend into the shelf,
receive auditory input from shelf axons. These hypotheses are longstanding but have never been confirmed, in part because the small size of
the structures and their physical proximity to each other hinders independent manipulation of the shelf and HVc. Auditory information may also
enter the VMP via the clHV-NIf-HVc pathway (Fig. 7.3). BOS selective
auditory responses and correlated activity in NIf have recently been
demonstrated (Janata and Margoliash 1999). NIf activity may be necessary
for HVc auditory responses (Boco and Margoliash 2001). NIf receives input
from clHV and possibly also from field L via the dendritic projections of a
distinct class of NIf neurons lying along the dorsorostral border of NIf with
L1 (Fortune and Margoliash 1995). Identification of sources of auditory
input into the VMP is of particular interest because it provides a neural
substrate for hypotheses about the origin of the well-known BOS selective
responses in these structures. The auditory inputs to HVc also provide the
basis for speculations that expand the functions of AFP structures beyond
their classic role in juvenile song learning and into adult song perception
(see Section 2.3.3).
The song system is associated with a series of cytoarchitectonically indistinct structures. These structures, such as the shelf ventral to HVc and
medial MAN, are physically close to cytoarchitectonically distinct songsystem nuclei and have patterns of connections similar to song-system
nuclei. Components of this indistinct system have also been observed in
several species of nonpasserine birds (Brauth et al. 1987; Brauth and
McHale 1988; Korzeniewska and Güntürkün 1990; Fortune and Margoliash
1995; see also Margoliash et al. 1994). Although the functions of this
pathway remain unknown, one possibility is that the song system arose as
a series of specializations of the indistinct pathway in relation to selection
pressures associated with vocal learning. If this is true, then the indistinct
pathway in oscines and other birds may mediate more general aspects of
362
T.Q. Gentner and D. Margoliash
for auditory information arriving via several parallel pathways from the Ov
complex in the thalamus (Fig. 7.3). Neurons in the shell of Ov also project
to the caudomedial portion of the neostriatum (NCM) (Durand et al. 1992;
Vates et al. 1996). The subregions of field L are densely interconnected and
project to the NCM and reciprocally to the lateral portion of the caudal
ventral hyperstriatum (clHV). The NCM and clHV share reciprocal connections with the caudal medial portion of HV (cmHV). Figure 7.3 provides
a schematic for this complicated pattern in songbirds.
Neurons in clHV, L1, and L3 also project to the neostriatum immediately
ventral to HVc, referred to as the “shelf” (Kelley and Nottebohm 1979).
Neurons in the shelf are auditory (Scheich et al. 1979a; Müller and
Leppelsack 1985), and it has been proposed that the shelf is a source of
auditory input to HVc. The projections of the shelf into HVc are extremely
sparse, however (L. Katz, cited in Margoliash 1987; Vates et al. 1996). One
proposition is that dendrites in caudal HVc, which extend into the shelf,
receive auditory input from shelf axons. These hypotheses are longstanding but have never been confirmed, in part because the small size of
the structures and their physical proximity to each other hinders independent manipulation of the shelf and HVc. Auditory information may also
enter the VMP via the clHV-NIf-HVc pathway (Fig. 7.3). BOS selective
auditory responses and correlated activity in NIf have recently been
demonstrated (Janata and Margoliash 1999). NIf activity may be necessary
for HVc auditory responses (Boco and Margoliash 2001). NIf receives input
from clHV and possibly also from field L via the dendritic projections of a
distinct class of NIf neurons lying along the dorsorostral border of NIf with
L1 (Fortune and Margoliash 1995). Identification of sources of auditory
input into the VMP is of particular interest because it provides a neural
substrate for hypotheses about the origin of the well-known BOS selective
responses in these structures. The auditory inputs to HVc also provide the
basis for speculations that expand the functions of AFP structures beyond
their classic role in juvenile song learning and into adult song perception
(see Section 2.3.3).
The song system is associated with a series of cytoarchitectonically indistinct structures. These structures, such as the shelf ventral to HVc and
medial MAN, are physically close to cytoarchitectonically distinct songsystem nuclei and have patterns of connections similar to song-system
nuclei. Components of this indistinct system have also been observed in
several species of nonpasserine birds (Brauth et al. 1987; Brauth and
McHale 1988; Korzeniewska and Güntürkün 1990; Fortune and Margoliash
1995; see also Margoliash et al. 1994). Although the functions of this
pathway remain unknown, one possibility is that the song system arose as
a series of specializations of the indistinct pathway in relation to selection
pressures associated with vocal learning. If this is true, then the indistinct
pathway in oscines and other birds may mediate more general aspects of
362
T.Q. Gentner and D. Margoliash