Memory deficits and retrieval processes in ALS¹

Abstract

Subtle neuropsychological deficits have been described in patients affected by amyotrophic lateral sclerosis (ALS) without dementia. Overall, selective impairment in memory function has been reported, but the source of memory impairment in ALS has yet to be defined. We performed neuropsychological screening in 20 ALS patients. Semantic encoding and post-encoding cue effects on the retrieval of word lists were investigated in the ALS patients and normal controls. Severity of memory impairment was correlated to cerebral blood perfusion detected by single photon emission computed tomography (SPECT). ALS patients showed moderate impairments in frontal and memory tests. Short-term memory was normal, while serial position retrieval of word lists with normal recency effect but poor primacy effect showed long-term memory deficit. ALS patients performed better in cued encoding than in cued post-encoding recall condition. In the cued post-encoding condition, the primacy effect in word list recall improved significantly in controls, but not in ALS patients, as compared with both the free recall and cued encoding conditions. SPECT hypoperfusion was observed in frontal and temporal areas in ALS patients. ALS patients showed a long-term memory deficit which did not improve in cued post-encoding condition as it does for controls. We hypothesize abnormal retrieval processes related to frontal lobe dysfunction which entails difficulties in generating stable long-memory traces at encoding.

Memory deficits in amyotrophic lateral sclerosis patients with dementia and degeneration of the perforant pathway

“…Because involvement of the perforant pathway has been considered to be one of the major lesions explaining contextual and episodic memory disturbance in AD [3], it is plausible that similar involvement of the perforant pathway, as we demonstrated in the present study, may explain similar memory deficits observed in some ALS patients with dementia. Currently, neuropsychological assessment of ALS patients with dementia is usually based on the assumption that cognitive abnormalities, including memory deficits, are related to frontal lobe dysfunction [20][21][22]. However, the present study indicates the possibility that the involvement of the perforant pathway is another candidate to explain cognitive dysfunction, especially memory deficits, sometimes found in ALS patients with dementia.…”

How predictive are temporal lobe changes of underlying TDP-43 pathology in the ALS-FTD continuum?

“…43 As for ALS, memory deficits have been controversial and most studies link memory impairment to executive dysfunction. 81,98,99 However, recent studies report authentic episodic memory deficits and implicate MTL structures, showing that memory impairment in non-demented ALS patients is not exclusively a disturbance of the executive functioning. 52,82,83,88,[100][101][102][103] Semantic memory Semantic memory is the knowledge of everyday objects and events and its loss is attributed to the deterioration of the ATL.…”

Cognitive and Behavioral Symptoms in ALSFTD

“…Disorientation and symptoms of disinhibition were not as prominent until later in the illness. Impairment on test of language function (eg, animal fluency) and episodic memory recall (eg, word lists) have been widely reported in both ALS 24,30 and in FTD variants. [31][32][33] Furthermore, these results are consistent with findings of anterior temporal lobe atrophy which has been well documented in ALSFTD.…”