Figure 6. Model of neural deficits in early AD. Neural connections associated with normal memory function involve frontal and temporal lobes. Somatosensory, visual, and auditory information proceed from primary and association cortex to prefrontal cortex, located in the posterior frontal lobe. This region plays a major role in executive function (ie, organizing and directing attention), as well as in working memory, acting as a "mental scratchpad" for short-term information needed to perform a task, such as dialing a phone number. Part of this information may be consolidated, branching to the medial temporal lobe region via the entorhinal cortex (medial temporal lobe) and into the hippocampal complex. Projections from the hippocampal complex can transfer long-term information back to prefrontal cortex. This back-and-forth pathway between prefrontal cortex and medial temporal lobes is known as the limbic loop and is considered important for emotional stability, learning and memory function, and regulation of autonomic and endocrine functions. It is precisely these areas that are particularly susceptible to the pathologic changes of AD (11). (Adapted, with permission, from reference 32.)