Cortical Integration In Processing Binocular Information And Coordinate-stimuli-dependent Plasticity

ObjectiveIn vivo extracellular recording techniques and blood oxygenation level dependent-magnetic resonance imaging (f MRI)were used to study spatial-temporal binocular integration and plasticity of orientation tuning property of striate neurons induced by coordinate binocular visual conditioning, to elucidate the visual mechanisms in processing binocular vision on the level of both individual cells and local circuits as well as different hierarchical cortical areas.Methods1. Spike rate and local field potential (LFP) gamma band (20-90Hz) power to monocular, synchronous and asynchrous(with a time delay from0-70ms) dichoptic presented gratings were assessed for binocular neurons in V1of kitten with in vivo extracellular recording under anaesthesia. Ocular dominance index (ODI) and binocular integration index (BII) of spike and LFP were quantitatively analyzed, the correlation between BII and ODI and the tuning curves of BII relative to delay time in dichotic trails were analysed.2. Spike rate and LFP gamma power of three kitten (1-1.2Kg,8-10weeks old) to monocular presented gratings were assessed for28neurons in V1with in vivo extracellular recording under anaesthesia and paralysis. Preferred orientation (PO) and orientation selection index (OSI) were computed. After conditioning with high frequency paired-gratings for13minutes, the shift direction%shift degrees (DS=APO-PPO,APO:after-conditioning orientation, PPO:before-conditioning orientation) and OSIs were investigated and compared.3. For all six subjects with normal vision, blood-oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to measure the neuronal response within visual cortical areas to binocular presentation of20A base-out prism, The activation areas and intensities were analyzed.Results1. Absolute values of spike-ODI was slightly larger than that of LFP-ODI.(t=2.606,P=0.021).A linear correlation between the ocular preferences of spike and LFP was found (R2=0.513, F=27.423, P=0.003). In dichotic trails, binocular facilitation with BII for spike was2.348±0.996, which is less than BII for LFP(3.678±1.974),(t=2.671, P=0.019). Binocular integration index for two signals were greater when monocular responses of both eyes were similar (P=0.035and P=0.124, respectively). Although both signals showed binocular facilitation when the time differences of dichoptic stimulus inputs from two eyes are relatively small (ie. mean time difference<9.7ms and15.6ms,respectively), less consistent trend was seen in binocular integration responses (BII) of spiking activity. As time differences increased, BII decreased exponentially and linearly for two signals, respectively.2.86%(24/28) of all neurons shift their preferred orientation toward the conditioning orientation (positive shift).14%(4/28) of all neurons shift their preferred orientation away from the conditioning orientation (negtive shift). Mean shift degree (DS) was7.978(SD=7.463,n=28). After conditioning, OSI were significantly improved.(1990±0.096vs.0.159±0.0780, t=-3.989, P<0.05, n=28)3. Polar striate cortex (Cuneus) and neighboring peristriate cortices (fusiform, lingual gyrus), middle temporal gyrus (MT), Angular and precunueus in parietal cortex, Frecentral gyrus, frontal eye fields (FEF) and supplementary eye field (SEF) in frontal cortex as well as specific nucleus in the thalamus and pons were activated.Conclusions1. Both Spiking activity and LFP exhibited binocular facilitation to synchronous presented dichoptic stimuli with significant facilitation induced by balanced monocular responses. Temporal coordinative and non-coordinative binocular inputs result in facilitation and rivalry respectively. Spiking activity and LFP reflect neural activity of different spatial scales and source components. These two signals follow different rules of tempo-spatial summation in early visual areas2. Orientation tuning property are fairly developed in primary visual cortex at the end of critical period. High frequency paired gratings conditioning of non-preferred orientation may modulate the orientation tuning property of neurons through the mechanism of Hebbian short-term synaptic3. Coactivated occipito-parietal and frontal visual areas are important in the processing and analysis of binocular disparity information in humans. These areas may play a role in modulating convergence eye movement involved in motor fusion through their projections to the brain stem motor centers.