Panagiotis Iliopoulos

Mnemonic discrimination (MD) is the ability to distinguish current experiences from similar memories. Research on the brain correlates of MD has focused on how regional neural responses are linked to MD. Here we go beyond this approach to investigate inter-regional functional connectivity patterns related to MD, its inter-individual variability and training-related improvement. Based on prior work we focused on medial temporal lobe (MTL), prefrontal cortex (PFC) and visual regions. We used fMRI to determine how connectivity patterns between these regions are related to MD before and after 2-weeks of web-based cognitive training. We found MD-related connectivity involving MTL-PFC-visual areas. Hippocampal-PFC connectivity was negatively associated with inter-individual variability in MD performance across two tasks. Hippocampal-PFC connectivity decrease was also linked to inter-individual variability in post-training MD improvement. Additionally, training led to increased connectivity from the lateral occipital cortex to the occipital pole area. Our results point to a hippocampal-PFC connectivity pattern that is a reliable marker of MD performance. This pattern is further related to MD training gains providing strong evidence for its role in distinguishing similar memories. Overall, we show that hippocampal-PFC connectivity constitutes a neural resource for MD that enables training-related improvement and may be targeted to enhance cognition.

Background: Mnemonic discrimination (MD), the ability to distinguish between similar but distinct memories, relies heavily on the integrity of key medial temporal lobe (MTL) regions. Aging is associated with declines in MD, but evidence suggests that cognitive training may help mitigate this decline. While prior research has shown that such training can improve MD performance, little is known about the relationship between these behavioral improvements and structural changes in specific brain regions. This study investigates whether an 8‐week web‐based MD training program enhances MD in older adults and examines whether these gains are linked to volumetric changes in MTL areas, including the A36 perirhinal area, a critical region for object and scene memory. Method: A total of 151 older adults (age M = 69.71 years, SD = 4.17) participated in an 8‐week web‐based MD training program. Participants were divided into three groups: object stimuli training (OG), scene stimuli training (SG), and an active control group (AC). A subset of OG (n = 33) and AC (n = 28) participants underwent pre‐ and post‐training 7T MRI scans (MP2RAGE 0.6 mm; T2w imaging: 0.4 x 0.4 x 1 mm along the hippocampal axis). The training required participants to differentiate between similar objects and scenes ('lures') and repeated items ('repeats’) in a progressively challenging MD task. Pre‐ and post‐training, participants completed a behavioral battery assessing MD and cognitive transfer effects. Volumetric changes in key MTL subregions, including the A36 perirhinal area, were assessed using the T2w ASHS algorithm for the MTL areas’ segmentations. Result: Behavioral results showed significant gains in MD in the OG and SG groups compared to the control group. Notably, within the object training but not the control group, volumetric increases in the left A36 perirhinal area were specifically linked to MD performance gains for scenes (ie. near transfer to scenes) but not objects. This suggests a robust link between structural plasticity and MD behavioral improvement. Conclusion: Our findings indicate that an 8‐week MD training program enhances memory performance in older adults and induces structural changes in the A36 perirhinal area, highlighting the potential for cognitive training to support brain health during aging.

Mnemonic discrimination (MD) is the ability to distinguish current experiences from similar memories. Research on the brain correlates of MD has focused on how regional neural responses are linked to MD. Here we go beyond this approach to investigate inter-regional functional connectivity patterns related to MD, its inter-individual variability and training-related improvement. Based on prior work we focused on medial temporal lobe (MTL), prefrontal cortex (PFC) and visual regions. We used fMRI to determine how functional connectivity patterns between these regions are related to MD before and after 2-weeks of web-based cognitive training. We identified a functional connectivity signature involving MTL-PFC-visual areas during successful MD. We found that hippocampal-PFC connectivity was negatively associated with interindividual variability in MD performance across two different tasks. Hippocampal-PFC connectivity decrease was also linked to interindividual variability in post-training MD improvement. Additionally, training led to increased connectivity from the lateral occipital cortex to the occipital pole area. Our results point to a hippocampal-PFC connectivity pattern which is a reliable, task-invariant, marker of MD performance. This pattern is further related to MD training gains providing causal evidence for its relevance in distinguishing similar memories. Overall, we show that hippocampal-PFC connectivity constitutes a neural resource for MD that enables training-related improvements and could be targeted in future research to enhance cognition.

Background: Episodic memory declines in old age. Successful memory relies on the process of mnemonic discrimination (MD) to establish distinct representations. However, the scope for improvement in older adults’ cognitive performance using cognitive training is poorly understood. Here we investigated whether cognitive training leads to improvement in MD and whether the benefits transfer across different stimulus types, tasks and cognitive functionsMethod: 112 older adults (age M = 67.96, SD = 3.86) completed an 8‐week web‐based MD training intervention divided into 3 groups: one group training with object stimuli (OG), one group training with scene stimuli (SG), one active control group. The training was based on the object‐scene MD task which involves differentiating similar objects and scenes (‘lures’; correct response: ‘new’) from repeated items ('repeats’, correct response: ‘old’). Stimuli were first presented in a 2‐back set‐size: the first two stimuli were new images, while each of the subsequent two could be either a lure or a repeat trial. Then set‐size increased progressively across the training. Pre‐ and post‐training, the subjects performed a behavioral session including the 2‐back object‐scene MD task and several other transfer tasks. The latter included the mnemonic similarity task (MST; i.e. a different MD task), a pattern completion, working memory, spatial learning, and navigation task.Result: Our results show a training‐induced improvement in the object‐scene MD task performance but not the MST. We found a bias‐corrected performance improvement (d prime) driven by the correct lures. Compared to the control group, the OG improved their MD performance in objects while the SG improved in scenes, but only the OG showed near transfer improvement to the non‐trained category (i.e. scenes). We found no significant training effect in other transfer tasks.Conclusion: An 8‐week cognitive training intervention led to MD improvement in the trained task. We found a same modality improvement with the OG improving in objects and the SG in scenes, and evidence of near transfer from object to scenes but not vice versa. Cognitive training can lead to MD improvement in older adults. Longer‐duration interventions are needed to assess far‐transfer effects.