Lesions in Ventral NLc

1
Vocal Performance and Plasticity Functions are
Segregated into Dorsal and Ventral Subdivisions
of a Single Nucleus in Budgerigars (Melopsittacus
undulatus)Georg F. Striedter and Kelly LeiDept
of Neurobiology Behavior and Center for the
Neurobiology of Learning Memory, UC Irvine
Lesions in Ventral NLc
Control Lesion in NLv
Introduction
By 14 days post-lesion, only a single call type
remains, but that call was never impaired.
No immediate vocal motor deficits and no gradual
shrinkage of vocal repertoire.
Figure Schematic of the vocal control circuitry
in budgerigars. The principal vocal motor
pathway is shown in red, the accessory vocal
control pathways in blue. Our lesions were
targeted at the dorsal and ventral divisions of
NLc (shown in purple).
Results Summary

• Nucleus AAc is a major vocal control nucleus in
  budgerigar (a.k.a. parakeets). It has dorsal and
  ventral divisions. Only the former is part of
  the principal vocal motor pathway (see Figure).
• Nucleus NLc projects topographically to AAc and
  is, therefore, likely to have dorsal and ventral
  divisions as well.
• Do dorsal and ventral NLc (NLc-d and NLc-v) have
  different functions? To answer this question,
  we lesioned them.

Lesion dorsal NLc bilaterally --gt Lower call
frequency, revealing harmonics
Methods
Similar lesion, same result the birds
repertoire is reduced to a single contact call
type
Making the Lesions
Lesion ventral NLc bilaterally --gt Shrink contact
call repertoire down to a single call type

• We made electrolytic lesions, targeted at either
  NLc-d or NLc-v, and aimed to make the lesions
  bilateral. All subjects were male.
• Our lesions disrupted fibers passing from NLc to
  Aac few other axons pass through NLc.

Lesion in Dorsal NLc
Conclusions

• Lesioning dorsal NLc causes immediate deficits in
  contact call production (similar to those
  observed after lesioning dorsal AAc). Therefore,
  dorsal NLc is part of the direct vocal motor
  pathway.
• Lesioning ventral NLc causes no immediate
  deficits in vocalization, but leads to a gradual
  shrinkage of the contact call repertoire.
  Therefore, ventral NLc is part of a circuit
  required for the maintenance of learned
  vocalizations.
• The vocal control circuits in budgerigars are
  very different from those in songbirds, but they
  share some design elements, notably a looping
  anterior forebrain circuit involved in the
  mainentance of learned vocalizations.

Analyzing the Contact Calls

• Vocalizations were recorded daily pre-lesion and
  up to 14 days post-lesion. Only contact calls
  were analyzed.
• Calls from a given day were compared by pairwise
  sonogram cross-correlations, followed by a
  k-means cluster analysis (the algorithm was
  instructed always to construct 3 clusters).
• Calls within a cluster were averaged, using the
  cluster centroids as the alignment references.
• In order to evaluate repertoire complexity, each
  set of cluster averages was itself averaged
  (weighted by calls/cluster). When the resultant
  3-cluster average resembles the individual
  cluster averages, then the birds repertoire
  contains only a single call type.

By day3, calls drop in frequency (revealing
hid-den harmonics), but repertoire does not
shrink.