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Effective Connectivity Analysis in Neural circuitry Underlying Perceptual and Value-based Memory

Fakharian, Mohammad Amin | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53248 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Amini, Arash; Ghazizadeh, Ali
  7. Abstract:
  8. Perceptual memory used in novel vs familiar discrimination is not only vital for the evaluation of environmental variations but also essential for learning, perception, and correcting behavioral policies. On the other hand, value-based memory which allows for discrimination of valuable objects among equally familiar ones also drives behavioral interactions and decision making. Although many studies have been conducted to address the neuronal association regarding each separately, the neural correspondence between perceptual and value-based memory is not scrutinized adequately. To this end, the differential neural activation in two macaque monkeys to unrewarded novel vs familiar fractals (>100 novel fractals) was obtained using fMRI and contrasted in the same monkeys to equally familiar fractals (>100) associated with large or small rewards (good and bad objects, respectively). In both conditions, a clear contrast in the activity of temporal and prefrontal cortices was found in both monkeys. Despite the overall similarity of activations, some clear differences were observed in sub-regions of ventral IT (Inferior Temporal) which showed strong perceptual memory modulation but limited value-based memory. Having analyzed the resting-state time series of subregions modulating perceptual and value-based memory, a functional connectivity graph is extracted using a causal search algorithm which is highly consistent with the anatomical expectations. Leveraging the spectral clustering algorithm, the extracted undirected weighted graph (from functional connectivity) is clustered. In both monkeys, a ventral-IT cluster was marked by strong novelty and little value coding, with the reverse pattern observed in a parietal cluster. On the other hand, a cluster of temporal and prefrontal areas (TP cluster) were similarly modulated by novelty and value, an effect that was underscored through dynamic causal modeling. Novelty and value co-coding was also seen in regions of striatum, amygdala and claustrum with functional connectivity to the TP cluster. While the co-activation of areas in the brain for both novelty and value can argue for a common underlying process such as attention, the existence of non-overlapping areas and dissimilar connectivity patterns argue for dissociable circuitry for perceptual and value-based object memory. Further studies about the neural mechanisms in these areas should reveal the mechanism of encoding and retrieval of both types of memories as well as their converging influence on attention
  9. Keywords:
  10. Value-Based Memory ; Perceptual Memory ; Brain Effective Connectivity ; Causal Graphical Models ; Causal Inference ; Spectral Clustering

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