ABSTRACT
In sensory perception, feedback connections from higher to lower levels in the processing hierarchy are considered to be of major importance. In the auditory system, connections from the auditory cortex to the inferior colliculus -the auditory midbrain- are well established, but the existence of inputs to the inferior colliculus from other, non-auditory,-cortical areas has not been systematically investigated. Using retrograde tracing we show that visual, somatosensory, motor, and prefrontal cortices all project extensively to the inferior colliculus. These connections are bilateral, with an ipsilateral dominance, but those from motor and prefrontal cortex show a less pronounced lateralization. Anterograde tracing reveals that cortical fibres terminate in all three subdivisions of the inferior colliculus, and target both GABAergic inhibitory, and putative glutamatergic excitatory neurons. These findings indicate that sound processing in the auditory midbrain is influenced by multiple sensory, behavioural, and executive cortical systems.
Footnotes
↵* Bas Olthof, Institute of Neuroscience, Faculty of Medical Sciences, Newcastle upon Tyne, NE2 4HH UK, bas.olthof{at}ncl.ac.uk
LIST OF ABBREVIATIONS
- AC
- auditory cortex
- AI
- agranular insular cortex
- Au1
- primary auditory cortex
- AuD
- secondary auditory cortex dorsal zone
- AuV
- secondary auditory cortex, ventral zone
- Cg1
- cingulate cortex area 1
- Cg2
- cingulate cortex area 2
- Den
- dorsal endopiriform nucleus
- DI
- dysgranular insular cortex
- DP
- dorsal peduncular cortex
- DZ
- primary somatosensory cortex dorsal zone
- Ect
- ectorhinal cortex
- GI
- granular insular cortex
- IL
- infralimbic cortex
- LO
- lateral orbital cortex
- M1
- primary motor cortex
- M2
- secondary motor cortex
- MC
- motor cortex
- MO
- medial orbital cortex
- PFC
- prefrontal cortex
- Prh
- perirhinal cortex
- PrL
- prelimbic cortex
- RSG
- retrosplenial granular cortex
- S1
- primary somatosensory cortex
- S1Tr
- primary somatosensory cortex trunk region
- S2
- secondary somatosensory cortex
- SC
- somatosensory cortex
- TeA
- temporal association cortex
- V1B
- primary visual cortex, binocular area
- V1M
- primary visual cortex, monocular area
- V2L
- secondary visual cortex, lateral area
- V2M
- secondary visual cortex, mediolateral area
- VC
- visual cortex
- VO
- ventral orbital cortex.
