Effects of Temporal Lobe Epilepsy on Retrograde Memory

Abstract

Summary:Purpose: In a previous investigation (Lah et al., 2004), we found deficits in retrograde memory in patients who had undergone temporal lobectomy (TL). In this study, we set out to determine whether such deficits are present before surgery in patients with temporal lobe epilepsy (TLE).Methods: Memory for public and autobiographic facts and events was assessed in patients with focal left-sided (n = 15) or right-sided (n = 14) TLE and healthy control subjects (n = 15). The impact of epilepsy and underlying cognitive deficits on retrograde memory also was examined.Results: Patients with left TLE demonstrated retrograde memory deficits across domains. Patients with right TLE showed defective recall only in the autobiographic domain. Young age at onset (younger than 14 years) was associated with greater difficulties in recall of famous events, and patients receiving polytherapy had significantly reduced recall of autobiographic events compared with those receiving monotherapy. In most cases, deficient memory for the past was associated with impairments in other cognitive skills, especially language abilities.Conclusions: In unoperated-on patients with TLE, we found deficits in retrograde memory that were similar to those seen after TL, with the pattern of deficits being influenced by side of lesion, anticonvulsant medication, and word-finding deficits. Unlike patients tested after right TL, patients with right TLE did not have difficulty recalling details of famous events, which raises the possibility that right TL results in a decline in this aspect of retrograde memory. Key Words: Retrograde memoryAutobiographic memory.Studies examining retrograde memory in patients who have undergone temporal lobectomy (TL) for intractable epilepsy have shown temporally extensive deficits on a range of retrograde memory tests (1,2). Kapur (3) argued that patients with epilepsy might have poor memory for the past because seizures affect memory storage in a variety of ways. He proposed that major seizures are likely to result in a period of retrograde amnesia. Even minor seizures may have a cumulative effect over time and result in a prolonged period of retrograde amnesia. Thus a longer history of seizures and possibly a history of generalized tonicclonic seizures would result in poorer retention of old memories and greater impairments on retrograde memory tests. Interestingly, however, in a previous study, we found that performance on retrograde memory tests after TL was not related to age at onset, duration of seizure disorder, or a history of generalized tonic-clonic seizures (2). We did find that patients who were still taking anticonvulsant medications showed greater impairment than those who were medication free. It seemed possible that the impact of a TL might outweigh effects related to seizure history.

Retrograde episodic and semantic memory impairment correlates with side of temporal lobe damage

“…Three other patients with damage confined to the frontotemporal regions of the right hemisphere (Calabrese et al, 1996;McCarthy & Warrington, 1992), or bilateral but predominant on the right side (Markowitsch et al, 1993), also manifested a more severe retrograde deficit in the retrieval of episodic than semantic memories. Finally, a more severe deficit in the autobiographical than in the semantic remote memory domain has been reported in a group of patients with right temporal lobe epilepsy (Lah et al, 2006). Not all of the reported neuropsychological evidence is, however, in keeping with the above-mentioned hypothesis of a dominance of the right and left cerebral hemispheres for the autobiographical and semantic aspects of the retrograde memory, respectively.…”

“…The semantic memory loss in this patient extended to vocabulary, arithmetic, and geographical knowledge, but his recollection of personally experienced events from his entire life was excellent. A more severe deficit of semantic than episodic retrograde memory in patients with left hemisphere temporal damage has also been reported in single case investigations by Markowitsch et al (1993) and Yasuda et al (1997) and in groups of epileptic patients before (Lah et al, 2006) and after left temporal lobectomy for the treatment of pharmacologically resistant epilepsy (Barr et al, 1990).…”

The neuroscience of remote memory

“…First, extended retrograde amnesia for autobiographical events has been reported in patients with temporal lobe epilepsy who have not had surgery [42]. HM's seizures began at age 10, and young age at onset is associated with especially severe retrograde amnesia [43]. Second, recent MRI scans document several abnormalities outside HM's medial temporal lobe, including cortical and subcortical atrophy, large amounts of abnormal white matter, and subcortical infarcts [44•].…”

Long‐term memory impairment in patients with focal epilepsy

“…Less research has been done on autobiographic memory in TLE (Lah et al, 2006). In particular, it is unclear whether reduced performance in tests of remote memory is due to encoding (anterograde) or retrieval (retrograde) deficits or both.…”