Cerebral Cortex Advance Access originally published online on December 22, 2004
Cerebral Cortex 2005 15(8):1207-1221; doi:10.1093/cercor/bhi003
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© Oxford University Press 2005; all rights reserved
Orientation and Direction Selectivity of Neurons in V1 of Alert Monkeys: Functional Relationships and Laminar Distributions
1 Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel, 2 Schepens Eye Research Institute, Boston, MA 02114, 3 Department of Ophthalmology, Harvard Medical School, Boston, MA 02115, USA and 4 Program in Neuroscience, Harvard Medical School, Boston, MA 02115, USA, 5 Current address: Department of Ophthalmology, Medical College of Georgia, Augusta, GA 30912-3402, USA
Address correspondence to Moshe Gur, Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa, 32000, Israel. Email: mogi{at}bm.technion.ac.il.
We studied orientation selectivity in V1 of alert monkeys and its relationship to other physiological parameters and to anatomical organization. Single neurons were stimulated with drifting bars or with sinusoidal gratings while compensating for eye position. Orientation selectivity based on spike counts was quantified by circular variance and by the bandwidth of the orientation tuning curve. The circular variance distribution was bimodal, suggesting groups with low and with high selectivity. Orientation selectivity was clearly correlated with spontaneous activity, classical receptive field (CRF) size and the strength of surround suppression. Laminar distributions of neuronal properties were distinct. Neurons in the output layers 2/3, 4B and 5 had low spontaneous activity, small CRFs and high orientation selectivity, while the input layers had greater diversity. Direction-selective cells were among the neurons most selective for orientation and most had small CRFs. A narrow band of direction- and orientation-selective cells with small CRFs was located in the middle of layer 4C, indicating appearance of very selective cells at an early stage of cortical processing. We suggest that these results reflect interactions between excitatory and inhibitory mechanisms specific to each sublamina. Regions with less inhibition have higher spontaneous activity, larger CRFs and broader orientation tuning. Where inhibition is stronger, spontaneous activity almost disappears, CRFs shrink, and orientation selectivity is high.
Key Words: behaving monkey • circular variance • primary visual cortex • receptive fields • spontaneous activity • V1 layers
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