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The hippocampus and cerebral neocortex receive massive cholinergic projections from the basal forebrain. These projections arise predominantly within the nucleus basalis of Meynert, also known as the Ch4 cell group. The cholinergic projection of the cerebral cortex plays a major role in sustaining episodic memory, attention, and experience-induced neuroplasticity. Progressive neurofibrillary degeneration in the nucleus basalis can be seen throughout the continuum that leads from normal aging to mild cognitive impairment and Alzheimer’s disease. The resultant perturbation of cortical cholinergic neurotransmission may contribute to the cognitive changes seen in normal aging and Alzheimer’s disease.
This article describes the structure, connections, and cell types of the amygdala in rodents and felines. In addition, the intrinsic membrane properties of amygdala neurons are described, along with the inhibitory pressures regulating their activity. Functionally, this article discusses the pathways that support the involvement of the amygdala in the acquisition and extinction of classically conditioned fear responses and the facilitation of memory by the amygdala in emotionally arousing conditions. First, the main components of the amygdala are reviewed, including their cell types and connectivity. Then considered are the intra-amygdaloid pathways supporting the involvement of the amygdala in the formation of emotional memories.
Executive functions are cognitive processes that critically involve the frontal lobes and enable us to accomplish goals and make decisions in everyday life. The brain regions responsible for some executive functions (spatial attention and memory) overlap with brain regions necessary for eye movements. Eye movements can be more reflexive (automatic) or more voluntary (willful). Voluntary eye movements, especially, have become an important tool with which to measure different aspects of executive functions in many human disorders. They also have been critical in differentiating subtypes and evaluating medication or treatment efficacy in clinical populations.
Neuroimaging and neurological investigations have shown that the frontal lobes play a critical role in human memory. In many aspects of memory, including working memory, learning of new information, and retrieval, the frontal lobes contribute to the guidance or executive control of memory processing. With the dynamic interplay of broad neural circuits, this brain region facilitates in the selecting, maintaining, updating, and retrieval of memory. In its absence, memories are disorganized and easily disrupted by interference or distraction. Terms such as executive control, top-down processing, and metacognitive control have been used to characterize the role of the frontal lobes in memory processes.