Anterograde Amnesia

Anterograde amnesia is characterized by a loss of memory for events which occurred following injury to the brain, whereas retrograde amnesia is characterized by a loss of memory for events which occurred before a brain injury (Graff-Radford, Tranel, Van Hoesen and Brandt, 1990; Jarrard, 2000). Anterograde amnesia is seen most frequently in patients who have sustained injuries to the medial temporal lobes or the diencephalon (Graff-Radford, Tranel, Von Hoesen, and Brandt, 1990). The medial temporal lobe contains the amygdala and the hippocampal formation, and animal experiments in primates have shown that damage to these two areas causes more severe anterograde amnesia (25). These two areas also send fibers to the diencephalon, and it is unclear if damage to the diencephalon affects the hippocampus and amygdala also.

Four patients with damage on both sides of the thalamus (in the diencephalon) were studied by imaging techniques and tests of mental function for more than a year to try and determine the effects of the damage on anterograde memory (Graff-Radford, Tranel, Van Hoesen and Brandt, 1990). Patients who had sustained damage to the mammillothalamic tract in the anterior thalamus which is related to the hippocampus, and the ventroamygdalofugal pathway which is related to the amygdala, developed amnesia (25). In monkeys, damage to either of these adjacent pathways often affects the other. The amnesia in humans with damage in this area of the diencephalon is charac

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his suggests, say the authors, the anterorhinal and perirhinal cortices support basic sensory memory functions for semantic but not episodic memories, which require additional processing by the hippocampal circuit (379). This is supported by post-mortem studies from anterograde amnesic patients showing bilateral pathology of the hippocampus alone. Koppelman et al (2001) found that anterograde memory loss correlated well with medial temporal, hippocampal, and thalamic measurements from MRI studies in a group of patients with organic amnesia from various diseases and 10 healthy controls (23). There was also an association between anterograde memory and hippocampal volume (28). On closer analysis, it was found that spatial memory correlated with hippocampal volume and total medial temporal volume, and temporal context memory correlated with whole brain, total frontal, and right frontal volumes (28). These results again suggest the hippocampal area is important in forming anterograde memories. In retrograde amnesia, there appears to be a temporally graded factor in that more recent memories are affected more than more distant memories (Squire and Clark, 2001). Data from animal experiments were assessed by these authors and

Category: Medical - A