Functional Neuroanatomy

These experiments are designed to investigate the functions of neuroanatomical pathways using methods such as lesions and immediate early gene (IEG) expression. In the experiment below an anatomical tracer, biotinylated dextran amines was placed in one vocal control nucleus, MO. . The tracer backfilled neurons projecting to MO and was used, therefore, to identify the afferent inputs to MO. At the end of the experiment, the subject was placed in a social setting in which he could listen to other birds and vocalize in response. This induced production of the zenk (zif 268, egr1, NGF1A, Krox24) protein, an immediate early response gene (IEG) protein (i.e. a transcriptional regulator). IEGs including zenk are known to couple exogenous stimulation such as that related to vocalization or hearing novel or meaningful sounds, to synthesis of proteins necessary for long term changes in neurons. Thus mapping of IEG expression can provide insights into the neuronal functions including those underlying perceptual and motor learning.

The figure depicts the main auditory streams to the vocal control nucleus MO in the budgerigar. For ease of readability pathways associated with the lateral MO are depicted on the right side of the drawing and those reaching the medial MO are decpited on the left side of the drawing. The reader is also referred to specific publications (Brauth et al, 2001; Brauth et al, 2002; Durand et al, 1997; Wild and Farabaugh, 1997; Striedter, 1994) for more information.

In these experiments we measured zenk protein expression in each auditory nucleus in response to presentation of an unfamiliar contact call and a contact call the birds were previously familiarized with due to repeated presentation.
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KEY FOR BUDGERIGAR AUDITORY STRUCTURES:

Field L (L1, L2, L3) - The primary telencephalic thalamo-recipient auditory area in birds. Field L is composed of three lamina, L1, L2 and L3. L2 receives most of the thalamic input. L1 and L3 are the more dorsally and ventrally situated lamina which give rise to the efferent projections of Field L. In parrots Field L projects laterally to a higher order area, NIVL (see below) as well as rostrally to the frontal lateral nidopallium (formerly neostriatum) (NFl) (see below). Such anterior projections (noted in red in the diagram) have not been identified in any other group of avian species and appear to constitute a key factor in the evolution of vocal learning in parrots.
Bas - Nucleus basorostralis, a polysensory area in the anterior telencephalon receiving trigeminal sensory information from the principal sensory nucleus of the trigeminal nerve and auditory information from the intermediate nucleus of the lateral lemniscus.
pBas - Peri-basorostralis area. Bas neurons project to immediately surrounding regions. Pbas neurons project directly to MO and exhibit very strong contact-call driven zenk protein expression.
NIVL - Nidopallium (formerly neostriatum) intermedium pars ventrolateralis - A higher order auditory area in the caudal telencephalon receiving input from Field L.
NFl - The frontal lateral nidopallium (formerly neostriatum). NFl receives input from the trigeminal and auditory portions of Bas and projects to neural fields near MO and to NLs. The confluence of projections from both Bas and Field L in NFl constitutes a distinctive feature of the parrot auditory system and appears to be a key element in the evolution of auditory-vocal learning in this species.
Mvl - The lateral surround of MO. Much of the telencephalic input to MO is derived from the immediate surround.
Mvm - The medial MO surround.
NLs - The supralaminar nucleus of the lateral nidopallium (formerly neostriatum). NLs receives input from NFl and projects to both NLc and MO.