Chareyron, L. J. | bioRxiv Science

bioRxiv2023

Using Recognition Testing to Support Semantic Learning in Developmental Amnesia

Patients with developmental amnesia (DA) have suffered hippocampal damage in infancy and subsequently shown poor episodic memory, but good semantic memory. It is not clear how patients with DA learn semantic information in the presence of episodic amnesia. However, patients with DA show well-developed recognition memory and these recognition abilities may support semantic learning. We present data from three experiments (two previously described in Elward & Vargha-Khadem, 2018). The first experiment showed that recall tests did not facilitate semantic learning. Patients with DA recalled only 35% of the learned information (controls recalled 80%). The second experiment indicated that multiple-choice recognition tests may facilitate learning. Patients with DA recalled 85% of the learned information. In experiment three, a patient with DA (aged 8 years) took part in a repeated-measures test so that recall learning and recognition learning could be directly compared. The results showed a clear benefit of recognition learning compared to recall learning (76% v. 35%). This finding indicates that young people with extensive hippocampal damage indeed utilise their recognition memory to support the integration of new information into their semantic system. This has important implications for the support of school-aged children with episodic memory difficulties.

neuroscience↗

bioRxiv2023

Paradoxical consequences of early hippocampal damage: greater atrophy is associated with better recall, working memory and visuospatial perception in developmental amnesia

Despite bilateral hippocampal damage dating to perinatal or early-childhood period, and severely-impaired episodic memory that unfolds in later childhood, patients with developmental amnesia continue to exhibit well-developed semantic memory across the developmental trajectory. Detailed information on the extent and focality of brain damage in these patients is needed to hypothesize about the neural substrate that supports their remarkable capacity for encoding and retrieval of semantic memory. In particular, we need to assess whether the residual hippocampal tissue is involved in this preservation, or whether the surrounding cortical areas reorganise to rescue aspects of these critical cognitive memory processes after early injury. We used voxel-based morphometry (VBM) analysis, automatic (FreeSurfer) and manual segmentation to characterize structural changes in the brain of an exceptionally large cohort of 23 patients with developmental amnesia in comparison with 32 control subjects. Both the VBM and the FreeSurfer analyses revealed severe structural alterations in the hippocampus and thalamus of patients with developmental amnesia. Milder damage was found in the amygdala, caudate and parahippocampal gyrus. Manual segmentation demonstrated differences in the degree of atrophy of the hippocampal subregions in patients. The level of atrophy in CA-DG subregions and subicular complex was more than 40% while the atrophy of the uncus was moderate (-23%). Anatomo-functional correlations were observed between the volumes of residual hippocampal subregions in patients and selective aspects of their cognitive performance viz, intelligence, working memory, and verbal and visuospatial recall. Our findings suggest that in patients with developmental amnesia, cognitive processing is compromised as a function of the extent of atrophy in hippocampal subregions, such that the greater the damage, the more likely it is that surrounding cortical areas will be recruited to rescue the putative functions of the damaged subregions. Our findings document for the first time not only the extent, but also the limits of circuit reorganization occurring in the young brain after early bilateral hippocampal damage.

neuroscience↗