Abstract
It is generally held that non-primary sensory regions of the brain have a strong impact on frontal cortex. However, the effective connectivity of pathways to frontal cortex is poorly understood. Here we microstimulate sites in the superior temporal and ventral frontal cortex of monkeys and use functional magnetic resonance imaging to evaluate the functional activity resulting from the stimulation of interconnected regions. Surprisingly, we find that, although certain earlier stages of auditory cortical processing can strongly activate frontal cortex, downstream auditory regions, such as voice-sensitive cortex, appear to functionally engage primarily an ipsilateral temporal lobe network. Stimulating other sites within this activated temporal lobe network shows strong activation of frontal cortex. The results indicate that the relative stage of sensory processing does not predict the level of functional access to the frontal lobes. Rather, certain brain regions engage local networks, only parts of which have a strong functional impact on frontal cortex.
Highlights
It is generally held that non-primary sensory regions of the brain have a strong impact on frontal cortex
The key question is: would a downstream sensory processing stage, such as voice-identity sensitive cortex in the aSTP, directly engage ventral frontal and orbital frontal cortex or would it interact with a local temporal lobe network to gain functional access to frontal cortex?
Given the large number of localizers and experiments conducted here, all the functional magnetic resonance imaging (fMRI) localizer and microstimulation experiments were conducted under anaesthesia using an established protocol
Summary
It is generally held that non-primary sensory regions of the brain have a strong impact on frontal cortex. 14), which represent the fourth or fifth anatomically defined stage of processing (Fig. 1a) This anterior/ventral temporal lobe region is known in humans[15] and macaque monkeys[16] to contain clusters of neurons[17] sensitive to voice content in communication sounds, such as the acoustical features associated with voice identity, that is, ‘who’ vocalized. The key question is: would a downstream sensory processing stage, such as voice-identity sensitive cortex in the aSTP, directly engage ventral frontal and orbital frontal cortex or would it interact with a local temporal lobe network to gain functional access to frontal cortex? Neuronal microstimulation of a given cortical site elicits an fMRI response in interconnected regions but Auditory cortical hierarchy (neuroanatomically defined)
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