Systems neuroscienceMultisensory processing via early cortical stages: Connections of the primary auditory cortical field with other sensory systems
Section snippets
Experimental procedures
Twelve young adult male Mongolian gerbils (Meriones unguiculatus), at least four months old and weighing 80–100 g, were used for this study. All experiments were approved by the animal care committee of Sachsen-Anhalt, Germany (No. 43.2-42502/2-2-325 IFN MD), in accordance with the NIH Guide for the Care and Use of Laboratory Animals (1996). Every attempt was made to minimize the number of animals used and to reduce their suffering at all stages of the study.
Results
The data presented here result from small injections of FD into the left AI. The injection sites were roughly spherical (mean diameter of 257±31 μm) and covered several cortical layers, usually supragranular, granular, and infragranular layers, but never reached layer VI or the white matter (Table 1). Four representative injection sites are illustrated in Fig. 1D. The approximate BFs of neurons at the injection sites ranged from 0.25 kHz to 12 kHz in the different cases (Table 1) and were
Summary and comparison with previous studies in the gerbil
The present study has shown, by use of the bidirectional and sensitive neuronal tracer FD, that AI of the gerbil (1) receives direct inputs from somatosensory, visual, and multisensory cortices, as well as from visual and multisensory thalamic and brainstem structures, and (2) has various projections to somatosensory, olfactory, visual, and multisensory cortical and subcortical brain regions. These connections are summarized in Fig. 4A. The results of the present study confirm some of the
Conclusions
In conclusion, it becomes increasingly apparent that the concept of purely unimodal processing in primary sensory cortices is wrong. Even these primary areas are not mere analyzers of properties of stimuli of their own modality but rather are involved in complex processing of other sensory, multisensory, and non-sensory information (for discussions see also Shimojo and Shams 2001, Cappe and Barone 2005, Scheich et al 2005, Schroeder and Foxe 2005).
Acknowledgments
We thank I. Forner, A. Gürke, and K. Gruss for their excellent histological assistance, Dr. W. Zuschratter for the technical support during the confocal laser scannings, M. Schild for reconstructing the ORIS data, and I. W. Stürmer for his investigation of the gerbil drumming behavior. We are also grateful to the three anonymous reviewers who provided helpful comments on a previous version of this paper.
Supported by the State Sachsen-Anhalt, BMBF, and DFG (SFB TR 31), Germany.
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