Anterograde versus Retrograde Effects of Damage to Identified Learning and Memory Systems during Acquisition, Retention, and Re-Acquisition of an Instrumental Visual Discrimination Task: Dorsal Striatum, Perirhinal Cortex, and Hippocampus.

Background: The goal of these experiments was to determine which learning and memory system(s) were necessary for the retention of visual discriminations and subsequent acquisition of a second problem. The dorsal striatum should be involved in the acquisition and expression of this task based on previous work implicating this region in instrumental learning and memory processes. The perirhinal cortex has been implicated in learning and memory processes associated with visual information like objects, and pictures and may also play a role in the acquisition and/or retention of visual discriminations.

Cholinergic depletion of the medial septum followed by phase shifting does not impair memory or rest-activity rhythms measured under standard light/dark conditions in rats.

The robustness of an individual's circadian rhythms has been correlated with the quality of their cognitive aging. This has been observed in both human and non-human animals and circadian rhythms are especially disrupted in patients with Alzheimer's disease (AD). It is possible that the circadian disruption observed in AD contributes to the cognitive decline in these patients; however, this has not been conclusively proven.

Selective lesion of medial septal cholinergic neurons followed by a mini-stroke impairs spatial learning in rats.

Reduced levels of hippocampal acetylcholine are a common finding in patients diagnosed with Alzheimer's disease, but it remains unclear what role this depletion plays in the development of dementia. It is possible that the reduced levels of acetylcholine increases the vulnerability of hippocampal neurons to future insults which could lead to neuronal death and cognitive impairment. One insult that is commonly observed in the demented elderly and often co-exists with Alzheimer's disease is stroke.

Reduced cholinergic status in hippocampus produces spatial memory deficits when combined with kainic acid induced seizures.

Alzheimer's disease is the most common form of dementia in North America today. Though many risk factors have been suggested to increase the likelihood of developing this disease, an accurate etiology has yet to be described. One of these risk factors commonly associated with Alzheimer's disease is the loss of cholinergic neurons of the medial septum that project to the hippocampus, leading to depletion in cholinergic activity.

Emergence of spatial impairment in rats following specific cholinergic depletion of the medial septum combined with chronic stress.

A consistent finding in patients suffering from Alzheimer's disease is a loss of the cholinergic neurons of the basal forebrain that project to the hippocampus. However, the role this depletion plays in the development of Alzheimer's disease remains unclear. The loss of this ascending neurotransmitter system could potentially render hippocampal neurons more susceptible to further insult, such as chronic stress, ultimately resulting in neuronal death and memory loss.