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 characterized by the loss of spoken and visual learning after the damage has occurred, and also retrograde amnesia, suggesting the diencephalon is involved in both processes.
A transient form of anterograde amnesia can occur following temporary ischemia to the thalamus (Goldenberg, Podreka, Pfaffelmeyer, Wessely and Deecke, 1991). A patient suffering from anterograde amnesia was examined using single-photon emission computed tomography (SPECT) and a radioactive tr...