Abstract
One of the main central processes affecting the cortical representation of conspecific vocalizations is the collateral output from the extended motor system for call generation. Before starting to study this interaction we sought to compare the characteristics of calls produced by stimulating four different parts of the brain in guinea pigs (Cavia porcellus). By using anaesthetised animals we were able to reposition electrodes without distressing the animals. Trains of 100 electrical pulses were used to stimulate the midbrain periaqueductal grey (PAG), hypothalamus, amygdala, and anterior cingulate cortex (ACC). Each structure produced a similar range of calls, but in significantly different proportions. Two of the spontaneous calls (chirrup and purr) were never produced by electrical stimulation and although we identified versions of chutter, durr and tooth chatter, they differed significantly from our natural call templates. However, we were routinely able to elicit seven other identifiable calls. All seven calls were produced both during the 1.6 s period of stimulation and subsequently in a period which could last for more than a minute. A single stimulation site could produce four or five different calls, but the amygdala was much less likely to produce a scream, whistle or rising whistle than any of the other structures. These three high-frequency calls were more likely to be produced by females than males. There were also differences in the timing of the call production with the amygdala primarily producing calls during the electrical stimulation and the hypothalamus mainly producing calls after the electrical stimulation. For all four structures a significantly higher stimulation current was required in males than females. We conclude that all four structures can be stimulated to produce fictive vocalizations that should be useful in studying the relationship between the vocal motor system and cortical sensory representation.
Highlights
IntroductionAnimal vocalizations are thought to be under the control of two distinct but overlapping motor systems: the first produces innate calls that are stereotypical and relatively invariant
As a prelude to studying the interaction between the vocal production pathways and the sensory representation [11], we sought to determine whether different brain structures were associated with specific calls, so that we could produce a call by electrical stimulation of a particular structure
In this figure the sequence of calls produced by stimulation of the anterior cingulate cortex (ACC) is shown in panel A over a period of almost 9 s
Summary
Animal vocalizations are thought to be under the control of two distinct but overlapping motor systems: the first produces innate calls that are stereotypical and relatively invariant. Between 11 and 13 calls have been identified in the guinea pig and the behavioural context of the calls has been identified both in the wild and in large caged colonies [4,5,6] Some of these calls seem to be consistently produced in a reflex response to a particular situation. As a prelude to studying the interaction between the vocal production pathways and the sensory representation [11], we sought to determine whether different brain structures were associated with specific calls, so that we could produce a call by electrical stimulation of a particular structure. These studies have led to the suggestion that particular calls may be associated with certain brain areas more than others [12, 14, 17]. All four of these brain structures were separately stimulated in an attempt to understand more about the role of each in call production
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