Enhancing memory performance after organic brain disease relies on retrieval processes rather than encoding or consolidation

Neuropsychological rehabilitation of memory performance is still a controversial topic, and rehabilitation studies have not analyzed to which stage of memory processing (encoding, consolidation, or retrieval) enhancement may be attributed. We first examined the efficacy of a computer training program for stroke patients, based on a previous study (Hildebrandt, Clausing, Janssen, Modden, 2007a) for memory-impaired patients of a rehabilitation unit and compared it with the standard group treatment. In a second randomized controlled experiment, we trained two groups of 15 patients with mild to moderate memory disorders, caused by organic brain lesions, with the same two treatment approaches. We used several standard tests to analyze improvement of memory functions, focusing on separate parameters for encoding, consolidation, and retrieval. We developed for that purpose a new word-list learning test, which allowed assessment of response to novelty and a systematic comparison of free recall after learning of semantically structured and nonstructured word lists. The first treatment experiment showed significant improvement of verbal learning for patients treated with the computer software program. The second experiment showed that memory improvement was based exclusively on retrieval processes, whereas no specific change was found for encoding and consolidation. However, the two groups of the second experiment showed no significant differences for the treatment, although the absolute scores pointed in the same direction as in the first experiment.