The Vocal Production Pathway
Intro
Vocalisations in Parrots are controlled by a number of specific brain regions called vocal nuclei that allow for both the learning and production of sound.
This is also how the 2 pathways for vocalisation are split:
- The vocal learning pathway (anterior pathway) is how sounds are learnt and remembered
- The vocal production (posterior pathway) is how sounds are produced
Anatomy
There are 7 vocal nuclei in the Parrot brain - these nuclei all occur in the telencephalon of the brain.
Of the 7 nuclei, there are 4 that are involved in the production of sound (long names not important)
These are:
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The oval nucleus of the mesopallium (MO)
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The oval nucleus of the anterior nidopallium (NAO)
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The central nucleus of the lateral nidopallium (NLC)
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The central nucelus of the anterior arcopallium (AAC)
A unique trait of Parrots is the shell tissue which surround the vocal nuclei, this tissue helps improve connectivity between the nuclei.
The size and effectivness of this shell tissue differs between species which contributes to the differing abilities of voclisations within Parrots.
Mechanism
The pathway to vocalisation starts with the oval nucleus of the mesopallium, the MO, shown in blue on figure 6, and the oval nucleus of the anterior nidopallium, the NAO, shown at the top in purple, which both send signals to the central nucleus of the lateral nidopallium, the NLC, and the central nucleus of the anterior arcopallium, the AAC, which are both shown in green. These signals then form a feedforward loop (between the NLC and the AAC) which causes the AAC to send specialised signals to brainstem vocal motor neurons, which in turn control the syrinx to create noise.
Step by Step-
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The MO and the NAO send impulses to the NLC and the AAC
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The NLC and the AAC form a feedforward loop
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The AAC send impulses to brainstem vocal motor neurons
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These specialised neurons stimulate the syrinx to create noise