Guide to the Anatomy of the Brain

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[In the brain, as in other complex systems, function follows form. Therefore, an understanding of learning and memory is critically dependent on a complete description of the anatomical organization of brain systems that support memory. Brain organization is composed at many levels, from cellular morphology to synapse types and their patterns of connection, to the cytoarchitecture of cortical and subcortical areas and the organization of neuronal types and input/output patterns, to major pathways and hierarchies of information processing. These levels of brain organization are surveyed in theO verviewsection that follows.

The fundamental alteration in plasticity that underlies memory occurs at the level of cellular anatomy and, in particular, synaptic structure. Therefore two sections of this guide provide a summary of our current knowledge about the structure ofN euronsandS ynapses. The section on neurons considers the major components of neurons and focuses on the cellular elements where plasticity occurs, specifically in the dendrites and synapses. This section also considers different neuron types and nature of connectivity patterns that form the circuitry in which plasticity exerts its effects on function. The section on synapses reviews the components of synapses and functionally distinct types of synapses. This section focuses on dendritic spines as the likely sites of plasticity that supports memory.

In other sections, this guide focuses on brain areas that play prominent roles in learning and memory. One area is the vast expanse of theC erebralC ortex. The cerebral cortex includes several functionally specific, hierarchically organized, areas and pathways that subserve specific perceptual, motor, emotional, and cognitive information processing functions. At the same time, these cortical areas are also the storehouses of memories for the specific information processed in those dedicated pathways. Therefore, understanding the functional organization of the cerebral cortex holds the key to characterizing the nature of the brain's representation of our accumulation of knowledge. TheO lfactoryC ortexis a part of the cerebral cortex that is simpler in its architecture than other cortical areas, and has served as a model system for anatomical and physiological studies and for the development of computational models of combined perceptual and memory processing.

The remaining sections consider a set of brain areas that are nodal points within brain pathways that support specific kinds of memory, or modulate memory. TheP erirhinalC ortexandH ippocampusare major components of the brain system that mediates "declarative memory," our capacity for conscious recollection of facts and events. TheA mygdalais a major component of a system for "emotional memory," the system that mediates assignments of affective value to otherwise neutral stimuli and initiates automatic responses to stimuli of acquired emotional significance. TheB asalG angliaandC erebellumare major components of distinct subsystems that mediate "procedural memory," the acquisition of skills, habits, and conditioned motor responses. TheB asalF orebrainplays a major role within the modulatory pathways that regulate attentional mechanisms that influence memory processing. The amygdala also plays a role in the modulation of memory processing in emotional circumstances. Thus each area plays a distinctive role in memory processing. In real life, they act in parallel to mediate the impact of experience on the brain's information-processing systems. This guide provides the reader with the anatomical framework in which these brain areas make their individual contributions to memory.]