Cortical visual areas in monkeys: location, topography, connections, columns, plasticity and cortical dynamics

The visual system is constantly challenged to organize the retinal pattern of stimulation into coherent percepts. This task is achieved by the cortical visual system, which is composed by topographically organized analytic areas and by synthetic areas of the temporal lobe that have more holistic processing. Additional visual areas of the parietal lobe are related to motion perception and visuomotor control. V1 and V2 represent the entire visual field. MT represents only the binocular field, and V4 only the central 30°–40°. The parietal areas represent more of the periphery. For any eccentricity, the receptive field grows at each step of processing, more at anterior areas in the temporal lobe. Minimal point image size increases towards the temporal lobe, but remains fairly constant toward the parietal lobe. Patterns of projection show asymmetries. Central V2 and V4 project mainly to the temporal lobe, while peripherals V2 (more than 30°) and V4 (more than 10°) also project to the parietal lobe. Visual information that arrives at V1 projects to V2, MT and PO, which then project to other areas. Local lateral propagation and recursive loops corroborate to perceptual completion and filling in. Priority connections to temporal, parietal and parieto-temporal cortices help construct crude early representations of objects, trajectories and movements

Functional MRI of neural plasticity and drug effect in the brain

Recent advances in magnetic resonance imaging (MRI) have opened up new perspectives for understanding brain function and its plasticity after damage or even in the process of learning and memory. Using functional MRI (fMRI), reorganization of the cortical representation can be detected after the peripheral nerves deafferentation or digit amputation. To detect the more trivial changes during learning and memory, we established two techniques. One is to use manganese as a contrast agent to detect minute reorganization of hippocampal mossy fiber after training with hidden platform in Morris water maze. The other technique detects the synchrony in fMRI signal among neural areas that represents functional connectivity. We demonstrated the spatial memory network can be visualized in water maze trained animal. Furthermore, we showed that synchrony rather than activity in the brain can be modulated by receptor targeted pharmaceuticals, which indicate a different drug mechanism. The translation of these methods will facilitate our understanding of brain plasticity, early diagnosis of dementia, and evaluation of drug efficacy