Daniel Jay Felleman - US grants

The goal of this research is to understand the neural mechanisms that underlie object perception in the primate cerebral cortex. The proposed experiments focus on areas V1, V2, and V4, which form the basis of low level and intermediate levels of object processing in the primate visual cortex. The first series of experiments will examine new aspects of the modular and submodular organizations of area V2 and their inputs from V1 and outputs to V4. Optical recording of intrinsic cortical signals will be used to characterize the functional architecture of V2 and to guide injections of neuroanatomical tracers into specific V2 modules or submodules. These studies will determine (1) the pattern of projections of 2-3 adjacent V2 thin stripes to V4, (2) whether V2 thin stripe submodules receive inputs from different populations of V1 blob and interblob cells and project to different portions of V4, and (4) whether V2 contains clusters of neurons that differ in their sensitivity to chromatic of orientation-specific surround antagonism. The second series of experiments will use optical recording of intrinsic cortical signals and conventional microelectrode recording to examine the functional architecture of area V4. These experiments will determine (1) the degree to which chromatic and orientation processing are segregated in V4, and (4) the functional architecture of chromatic and orientation-specific surround antagonism in V4. Overall, these experiments will provide new insight into the modular and submodular organizations of areas V1 and V2 and will lead to better understanding of the functional architecture of V4. The long-term goal of this research is to link the functional properties of specific V4 modules to their connections with V1, V2 and other cortical areas. These experiments lay the groundwork for future investigations of specific V4 modules and their relationship with individual cortical areas of inferotemporal cortex.

eye disorder; eye; computer program /software; biomedical facility; vision;

computer graphics /printing; computer program /software; data collection methodology /evaluation

Developmental disorders such as autism offer a unique opportunity to identify important brain structures and functional circuits that underlie complex, perceptual, cognitive, and social behaviors. The proposed multi-disciplinary program, utilizing behavioral testing (Project I) and MRI spectroscopy in autistic children (Project II), and behavioral, MRI-spectroscopic, and neuroanatomical studies in monkeys (Projects II and III), offers a comprehensive analysis of testable animal model of human autism. According to this hypothesis, early damage to the amygdala-orbitofrontal circuit causes a developmental impairment characterized by disturbances in social, emotional, and cognitive behavior. Project IV will evaluate the degree to which the infant responds to injury to the orbitofrontal-amygdala circuit. In order to evaluate fully the possible mechanisms of functional reorganization following this neonatal brain damage, the normal infant and normal adult patterns of cortico-limbic connections will be evaluated using modern neuroanatomical pathways tracing techniques. These patterns of connections will then be correlated with the immunocytochemical development of this circuit and closely related structures. Next, the patterns of cortico-limbic connections with be evaluated in adult monkeys that received either early or late lesions of the amygdala or orbitofrontal cortex. These results will establish the degree to which the developing nervous system can utilize compensatory mechanisms to stabilize developmentally transient neural pathways, to recruit new pathways between weakly associated structures, or to recruit new target structures into functional cortico-limbic circuits. Overall, this research will make a significant contribution towards our understanding of the neurobiological bases of pervasive developmental disorders.

ABSTRACT NOT PROVIDED

Area V4 is a key component of primate visual cortex that is involved in many aspects of 'intermediate'processing including higher-order shape processing, color constancy, and attention. V4 performs more complex computations than lower areas V1 or V2, but it does not complete object analysis that occurs in the temporal lobe. Despite considerable knowledge about the properties of individual V4 neurons, little is known about how simple and more complex visual features are represented by populations of neurons in V4. Recent experiments indicate that V4 orientation-preferred regions consist of small iso-orientation clusters that systematically shift to form orientation maps. Similarly, V4 color-preferring regions consist of small iso-hue clusters that shift systematically to form pinwheel-, line-, or angle-shaped hue maps. Most importantly, these orientation- and color-preferring maps partially overlap each other, resulting in both color or orientation single-feature modules and color-orientation feature-conjunction modules. In the proposed experiments, intrinsic cortical imaging will determine quantitatively, how preferred color and orientation preference and selectivity are represented in V4 and whether these features are organized into single-feature and feature-conjunction modules. Electrophysiological recording will determine the neuronal bases of these feature maps. Since V4 modules are expected to be small (~0.5-1 mm across), closely spaced microelectrode arrays will optimize the detection of systematic differences in neuronal color and orientation tuning across the cortex. V4 receives dense, largely segregated inputs from V2 thin and interstripes that are thought to convey color and shape information, respectively. However, it remains largely unknown how these inputs contribute to the neuronal properties and functional architecture of V4. In these experiments, distinguishable neuroanatomical tracers will be injected into two or more functionally characterized V4 modules to determine their specific patterns of connections with V2. The long-term goal of this research is to determine how different visual features are represented at different hierarchical levels of visual cortex and to determine how these architectures contributes to object recognition and memory.