Modulating Long Term Memory at Late-Encoding Phase: An rTMS Study.

Despite a huge effort of the scientific community, the functioning of Long-Term Memory (LTM) processes is still debated and far from being elucidated. Functional and neurophysiological data point to an involvement of Dorsolateral Prefrontal Cortex (DLPFC) in both encoding and retrieval phases. However, the recently proposed Explicit/Implicit Memory Encoding and Retrieval (EIMER) model proposes that LTM at the encoding phase consists of anatomically and chronologically different sub-phases. On this basis, we aimed to investigate the role of right DLPFC during a late-encoding phase by means of low-frequency rTMS. Thirty right-handed healthy subjects were divided into three experimental groups. Inhibitory rTMS was applied over right-DLPFC immediately after the encoding phase (Late-Encoding Group) or before recognition phase (Pre-Recognition Group), 24 h after, of an LTM task. Both groups also received sham stimulation during the non-target phase, while the third group (Sham Group) received only sham stimulation in both phases. The Late-Encoding Group collected a lower number of correct responses compared with Sham Group (p = 0.00), while Pre-Retrieval Group increased accuracy as compared to the Sham Group (p = 0.0). rTMS-inhibition of the right DLPFC seems able to interfere with LTM memory performances when delivered at a late stage of the encoding phase, with opposite effects at the pre-retrieval phase.

Stuck in the here and now: Construction of fictitious and future experiences following ventromedial prefrontal damage.

There is increasing interest in uncovering the cognitive and neural bases of episodic future thinking (EFT), the ability to imagine events relevant to one's own future. Recent functional neuroimaging evidence shows that the ventromedial prefrontal cortex (vmPFC) is engaged during EFT. However, vmPFC is also activated during imagination of fictitious, atemporal experiences. Therefore, its role in EFT is currently unclear. To test (1) whether vmPFC is critical for EFT, and (2) whether it supports EFT specifically, or, rather, construction of any complex experience, patients with focal lesions to vmPFC (vmPFC patients), control patients with lesions not involving vmPFC, and healthy controls were asked to imagine personal future experiences and fictitious experiences. Compared to the control groups, vmPFC patients were impaired at imagining both future and fictitious experiences, indicating a general deficit in constructing novel experiences. Unlike the control groups, however, vmPFC patients had more difficulties in imagining future compared to fictitious experiences. Exploratory correlation analyses showed that general construction deficits correlated with lesion volume in BA 11, whereas specific EFT deficits correlated with lesion volume in BA 32 and BA 10. Together, these findings indicate that vmPFC is crucial for EFT. We propose, however, that different vmPFC subregions may support different component processes of EFT: the most ventral part, BA 11, may underlie core constructive processes needed to imagine any complex experience (e.g., scene construction), whereas BA 10 and BA 32 may mediate simulation of those specific experiences that likely await us in the future.