Accelerated long-term forgetting: Design and validation of a neuropsychological tool in healthy subjects and diagnostic accuracy in a group of subjects with severe acquired brain injury.

Objective: Accelerated Long-term Forgetting (ALF) is a phenomenon characterized by abnormal memory forgetting over hours or days, despite normal initial acquisition. Because standardized memory assessments typically test memory retention over delays of up to 30 minutes, ALF may be undetected.

Methods: The first Experiment of the present study was aimed to validate, in a sample of healthy subjects (n = 54, 20 to 79 years old), a long-term verbal and visuospatial memory procedure, using common tests but administered at extended intervals. In Experiment 2, we aimed to explore ALF pattern in a sample of patients with severe Acquired Brain Injury (sABI) who subjectively complained of memory difficulties and nevertheless obtained normal or only mildly deficient scores on traditional memory tasks (n = 10).

Results: Results of Experiment 1 showed that both the verbal and visuo-spatial memory tasks proved to be valid and effective at illustrating the phenomenon of forgetting along the time intervals considered. Moreover, a significant association was found between higher saving scores passing from the 30 min to the 24 hr interval of the verbal test and the score obtained on a questionnaire assessing the subjective feeling of memory functioning. Results of Experiment 2 showed that patients with sABI obtained reduced 30 m-24hr saving scores on the verbal test as compared to healthy controls despite comparable forgetting at earlier and later delays.

Conclusions: These findings support the utility of extended memory assessment, thus the need for validation of specific diagnostic tools in clinical practice.