Cortical Feedforward and Cortical Feedback Neural Systems in Alzheimer’s Disease

Summary

This chapter provides a brief review of the principles of organization that relate to long association axons systems in the cerebral cortex. In particular, feedforward sensory systems are traced to their endstations in the entorhinal/hippocampal cortex, the amygdala and the nucleus basalis of Meynert. Feedback projections to the cerebral cortex from these limbic structures are also highlighted. These cortical connections are discussed relative to the topography of pathology in Alzheimer’s disease and the fact that neurofibrillary tangles invariantly affect these cortical systems early in the illness. It is argued that the co-occurrence of pathology in the endstations of feedforward systems and the origin of initial feedback systems is coupled tightly to alterations of memory in Alzheimer’s disease and other cognitive changes associated with the disorder. Widespread association cortex pathology, seen at endstage Alzheimer’s disease, is related likely to degree, or density, of impairment in the disorder, but may be secondary to the behaviorally disruptive consequences of early and invariant limbic system pathology.