Spatial Dstribution of Response Latency in the Anterior Field of the Auditory Cortex of the Guinea Pig.

By studying the efferent projections of five auditory areas in the guinea pig cortex, we sought evidence that the larger fields can be divided into subareas based on unique patterns of cortical connections. Small extracellular injections of biocytin were made in combination with evoked potential mapping or single-unit analysis and histochemical determination of cortical landmarks. The two core fields, primary (AI) and dorsocaudal (DC), are partially surrounded by six adjacent belt areas, leaving two gaps: one at the rostral edge of AI and the other at the dorsal edge. All of the areas studied projected to their nearest neighbors, but AI was the only area to project to all seven of the other auditory areas. The caudal, high-frequency (more than 4 kHz) end of AI had different projections from the rostral, low-frequency (less than 1.5 kHz) end, and there was no evidence of connections between the two ends. Each end had separate dorsal and ventral projections. The two ends of AI may be working independently. By contrast, area DC had strong connections between its high- and low-frequency ends and it may be involved in auditory/visual integration. The dorsorostral belt (DRB) was subdivided into two zones on the basis of its projections: the more rostral part appears to overlap the second somatosensory area and be bimodal, while the caudal part has stronger auditory connections. The small belt area (area S) had separate physiological and anatomical properties from the rest of the rostral belt.

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Interconnections of auditory areas in the guinea pig neocortex

Wallace

Rutkowski

Palmer

2002

Exp Brain Res

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Functional subdivisions in low-frequency primary auditory cortex (AI)

Wallace

Palmer

2009

Exp Brain Res

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We wished to test the hypothesis that there are modules in low-frequency AI that can be identified by their responsiveness to communication calls or particular regions of space. Units were recorded in anaesthetised guinea pig AI and stimulated with conspecific vocalizations and a virtual motion stimulus (binaural beats) presented via a closed sound system. Recording tracks were mainly oriented orthogonally to the cortical surface. Some of these contained units that were all time-locked to the structure of the chutter call (14/22 tracks) and/or the purr call (12/22 tracks) and/or that had a preference for stimuli from a particular region of space (8/20 tracks with four contralateral, two ipsilateral and two midline), or where there was a strong asymmetry in the response to beats of different direction (two tracks). We conclude that about half of low-frequency AI is organized into modules that are consistent with separate "what" and "where" pathways.

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A ventrorostral belt is adjacent to the guinea pig primary auditory cortex

1999

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The previously defined anterior area (A) of guinea pig auditory cortex has been divided into a large dorsal portion identified as the primary area (AI) and a smaller ventrorostral belt (VRB). This division is based on: (1) the much longer response latency of units in VRB (21.7 ms) than AI (14.1 ms); (2) the absence of pure onset units in VRB (i.e. units that lacked a sustained response), which are common in AI; (3) the weakness of noise-induced evoked potentials in VRB compared to AI; (4) units in VRB had lower thresholds and stronger phase locking to amplitude modulated stimuli than in AI.

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Spatial Dstribution of Response Latency in the Anterior Field of the Auditory Cortex of the Guinea Pig.

Cited by 5 publications

References 15 publications

Interconnections of auditory areas in the guinea pig neocortex

Interconnections of auditory areas in the guinea pig neocortex

Functional subdivisions in low-frequency primary auditory cortex (AI)

A ventrorostral belt is adjacent to the guinea pig primary auditory cortex

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