The nature of remote memory impairment in patients with medial temporal lobe damage is the subject of some debate. While some investigators have found that retrograde amnesia in such patients is temporally graded, with relative sparing of remote memories (Squire and Alvarez, 1995), others contend that impairment is of very long duration and that remote memories are not necessarily spared (Sanders and Warrington, 1971;Nadel and Moscovitch, 1997). In this study, remote memory was assessed in 25 patients with unilateral temporal lobe epilepsy and 22 non-neurologically impaired controls using the Autobiographical Memory Interview (Kopelman et al., 1989). Results indicate that patients have impaired personal episodic memory but intact personal semantic memory. The impairment extends even to the most remote time periods in early childhood, long before seizure onset in many patients. As well, patients awaiting temporal lobectomy for control of seizures perform as poorly as those who have already undergone resective surgery. These results support the hypothesis that temporal lobe damage or dysfunction, caused by recurrent seizures or surgical excision, results in extensive retrograde amnesia for personal episodic memories. Interestingly, patients with radiological evidence of hippocampal sclerosis were not significantly more impaired than those without obvious sclerosis. These results indicate that even minimal damage to medial temporal lobes results in significant impairment to autobiographical episodic memory. These findings are more compatible with a memory loss or retrieval deficit rather than a consolidation account of remote memory impairment. Key words: remote memory; episodic memory; epilepsy; temporal gradient; multiple trace theory; consolidation; autobiographical memoryThe study of remote memory is key to understanding the role of the hippocampal complex in memory consolidation. The development of a standardized test, the Autobiographical Memory Interview (AMI), by Kopelman et al. (1989Kopelman et al. ( , 1999 has made it easier to assess personal remote memory reliably in humans. The AMI measures personal semantic and episodic memories from different time periods-childhood, early adulthood, and the recent past-permitting examination of the possible differential effects of brain damage on these two types of autobiographical memory.In keeping with earlier observations (Ribot, 1882;Burnham, 1903;Scoville and Milner, 1957) Squire (1992) and Squire and Alvarez (1995) noted a temporal gradient to retrograde amnesia (RA) associated with medial temporal damage with the most remote memories differentially spared. He concluded that the hippocampus is involved in the establishment of new memories and their temporary storage but that over time these memories become independent of the hippocampus through consolidation. Once consolidation is complete, the memory trace resides elsewhere, rendering the hippocampus unnecessary for retrieval. According to consolidation theory, patients with temporal lobe epilepsy (TLE) and d...
Phonological and semantic aspects of language were examined in patients with unilateral temporal lobe epilepsy (TLE) and healthy controls using functional MRI. We expected to replicate previous findings in healthy individuals showing relatively greater activation in frontal regions for phonological compared with semantic processing, and greater activation in temporal regions for semantic compared with phonological processing. We hypothesized that differences between patients with left TLE and healthy controls would be found in the pattern of left temporal cortical activation associated specifically with semantic processing. Patients with right TLE were included as a seizure control group. All TLE patients previously showed left hemisphere language dominance on intracarotid sodium amytal studies. Greater blood oxygen level dependent activation was found during phonological processing compared with semantic processing in frontal regions for healthy participants but, contrary to expectation, semantic processing did not lead to increased temporal lobe activity relative to phonological processing. Furthermore, no differences between left temporal patients and controls were found specifically in left temporal cortex. Rather, patients with left temporal seizure foci showed significantly greater left dorsolateral prefrontal activity compared with controls, as well as increased signal change in left inferior frontal and right middle temporal gyrus. Surprisingly, patients with right, but not left, TLE showed poorer performance on the linguistic tasks compared with controls, as well as a decrease in right superior temporal activation. The results converge with studies of dyslexic patients showing increased left frontal activity in the presence of left temporal dysfunction and are suggestive of both inter- and intra-hemispheric functional reorganization of language representation in left TLE.
DBS-f was safe. Additional study of mechanisms of action and methods for titrating stimulation parameters will be needed to determine if DBS has potential as an AD treatment. Future efficacy studies should focus on patients over age 65.
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