Visual perspective in autobiographical memories of self-incongruent episodes.

It is widely assumed that autobiographical memory relies on an integration of episodic memory with the self-model. We hypothesise that self-memory integration depends critically on self-congruence. More specifically, self-incongruent experiences such as those that elicit shame or guilt may be more difficult to integrate. Self-incongruence may affect both the semantic reports of memories and their phenomenological characteristics, in particular their visual perspective (1PP or 3PP, i.e., field or observer perspective), their affective valence, and their perceived centrality. Diary based memories were assigned to 4 categories (shame, guilt, negative, neutral) and were rated for the different phenomenological dimensions. We used a deep neural network, univariate and multilevel models to assess differences and relationships between different variables. We found that memories that elicited shame (but not guilt) showed more pronounced 3PP as compared to other experiences. Shameful episodes also elicited the most pronounced negative affect. A multilevel analysis revealed that the amount of shame that an episode elicited, and its semantic similarity with shame episodes, predicted higher 3PP, while affective valence did not. Our results show that self-incongruence affects memories both at the level of their semantic reports and their phenomenology, and thus contributes to a mechanistic understanding of self-memory integration.

Probing the relevance of the hippocampus for conflict-induced memory improvement.

The hippocampus plays a key role for episodic memory. In addition, a small but growing number of studies has shown that it also contributes to the resolution of response conflicts. It is less clear how these two functions are related, and how they are affected by hippocampal lesions in patients with mesial temporal lobe epilepsy (MTLE). Previous studies suggested that conflict stimuli might be better remembered, but whether the hippocampus is critical for supporting this interaction between conflict processing and memory formation is unknown. Here, we tested 19 patients with MTLE due to hippocampal sclerosis and 19 matched healthy controls. Participants performed a face-word Stroop task during functional magnetic resonance imaging (fMRI) followed by a recognition task for the faces. We tested whether memory performance and activity in brain regions implicated in long-term memory were modulated by conflict during encoding, and whether this differed between MTLE patients and controls. In controls, we largely replicated previous findings of improved memory for conflict stimuli. While MTLE patients showed response time slowing during conflict trials as well, they did not exhibit a memory benefit. In controls, neural activity of conflict resolution and memory encoding interacted within a hippocampal region of interest. Here, left hippocampal recruitment was less efficient for memory performance in incongruent trials than in congruent trials, suggesting an intrahippocampal competition for limited resources. They also showed an involvement of precuneus and posterior cingulate cortex during conflict resolution. Both effects were not observed in MTLE patients, where activation of the precuneus and posterior cingulate cortex instead predicted later memory. Further research is needed to find out whether our findings reflect widespread functional reorganization of the episodic memory network due to hippocampal dysfunction.

Resection of cerebellar tumours causes widespread and functionally relevant white matter impairments.

Several diffusion tensor imaging studies reveal that white matter (WM) lesions are common in children suffering from benign cerebellar tumours who are treated with surgery only. The clinical implications of WM alterations that occur as a direct consequence of cerebellar disease have not been thoroughly studied. Here, we analysed structural and diffusion imaging data from cerebellar patients with chronic surgical lesions after resection for benign cerebellar tumours. We aimed to elucidate the impact of focal lesions of the cerebellum on WM integrity across the entire brain, and to investigate whether WM deficits were associated with behavioural impairment in three different motor tasks. Lesion symptom mapping analysis suggested that lesions in critical cerebellar regions were related to deficits in savings during an eyeblink conditioning task, as well as to deficits in motor action timing. Diffusion imaging analysis of cerebellar WM indicated that better behavioural performance was associated with higher fractional anisotropy (FA) in the superior cerebellar peduncle, cerebellum's main outflow path. Moreover, voxel-wise analysis revealed a global pattern of WM deficits in patients within many cerebral WM tracts critical for motor and non-motor function. Finally, we observed a positive correlation between FA and savings within cerebello-thalamo-cortical pathways in patients but not in controls, showing that saving effects partly depend on extracerebellar areas, and may be recruited for compensation. These results confirm that the cerebellum has extended connections with many cerebral areas involved in motor/cognitive functions, and the observed WM changes likely contribute to long-term clinical deficits of posterior fossa tumour survivors.

Reduced hippocampal recruitment during response conflict resolution in mesial temporal lobe epilepsy.

Recent evidence suggests that the human hippocampus (HC) is not only involved in the processing of motivationally relevant approach-avoidance conflicts but is also engaged in the resolution of more general response conflicts as measured in the Stroop paradigm. Here we investigated whether neural activity in the HC is necessary for successful response conflict resolution. We compared hippocampal recruitment during an auditory Stroop paradigm in 20 patients with mesial temporal lobe epilepsy (MTLE) due to hippocampal sclerosis and 20 age-matched healthy controls using functional magnetic resonance imaging (fMRI). We analyzed hippocampal activation and behavioral performance in conflict trials relative to non-conflict trials. Moreover, functional connectivity (FC) analyses with left and right HCs as seeds were performed. Subjects' regional gray matter volumes were analyzed based on high-resolution T2-weighted MRI scans. The current study replicated previous results showing increased activation in left HC during the processing of conflict trials in healthy subjects. By contrast, MTLE patients showed higher behavioral costs of response conflict resolution and reduced conflict-related HC activation. In patients with left MTLE, left HC activation was predictive of faster conflict-related response times (RTs). By contrast, right HC activation was related to RT slowing, suggestive of a maladaptive compensation attempt in MTLE patients. Our results provide evidence that left hippocampal activation is required for the successful resolution of response conflicts.

The neural mechanism of fluency-based memory illusions: the role of fluency context.

Recognition memory judgments can be influenced by a variety of signals including fluency. Here, we investigated whether the neural correlates of memory illusions (i.e., misattribution of fluency to prior study) can be modulated by fluency context. Using a masked priming/recognition memory paradigm, we found memory illusions for low confidence decisions. When fluency varied randomly across trials, we found reductions in perirhinal cortex (PrC) activity for primed trials, as well as a (pre)cuneus-PrC (BA 35) connectivity. When the fluency context was unchanging, there was increased PrC activity for primed trials, with the (pre)cuneus showing greater connectivity with PrC (BA 36). Thus, our results tentatively suggest two neural mechanisms via which fluency can lead to memory illusions.

Priming for novel object associations: Neural differences from object item priming and equivalent forms of recognition.

The neural substrates of associative and item priming and recognition were investigated in a functional magnetic resonance imaging study over two separate sessions. In the priming session, participants decided which object of a pair was bigger during both study and test phases. In the recognition session, participants saw different object pairs and performed the same size-judgement task followed by an associative recognition memory task. Associative priming was accompanied by reduced activity in the right middle occipital gyrus as well as in bilateral hippocampus. Object item priming was accompanied by reduced activity in extensive priming-related areas in the bilateral occipitotemporofrontal cortex, as well as in the perirhinal cortex, but not in the hippocampus. Associative recognition was characterized by activity increases in regions linked to recollection, such as the hippocampus, posterior cingulate cortex, anterior medial frontal gyrus and posterior parahippocampal cortex. Item object priming and recognition recruited broadly overlapping regions (e.g., bilateral middle occipital and prefrontal cortices, left fusiform gyrus), even though the BOLD response was in opposite directions. These regions along with the precuneus, where both item priming and recognition were accompanied by activation, have been found to respond to object familiarity. The minimal structural overlap between object associative priming and recollection-based associative recognition suggests that they depend on largely different stimulus-related information and that the different directions of the effects indicate distinct retrieval mechanisms. In contrast, item priming and familiarity-based recognition seemed mainly based on common memory information, although the extent of common processing between priming and familiarity remains unclear. Further implications of these findings are discussed.

The kinds of information that support novel associative object priming and how these differ from those that support item priming.

We investigated how the information that supports novel associative and item object priming differs under identical study/test conditions. In Experiments 1 and 2, participants rated the meaningfulness of sentences linking two object pictures at study. At test, they performed either a size judgement or an associative recognition memory task on intact, recombined and novel picture (Experiment 1) or word (Experiment 2) associations. Associative priming was modulated by subjective meaningfulness of the encoded links, and depended on study/test perceptual overlap. In contrast, item priming was neither affected by the meaningfulness of the sentences nor by study/test changes in the stimulus presentation format. Associative priming and recognition were behaviourally dissociated, and associative recognition was probably too slow to have seriously contaminated associative priming. In Experiment 3, participants performed a perceptually oriented task during both experimental phases, and both associative and item priming were observed. These results suggest that associative priming depends on stored associative semantic and perceptual information when the test task requires flexible retrieval of associative information. Under the same conditions, item priming may only require activation of items' semantic properties. When both study and test tasks stress perceptual processing, retrieval of perceptual information is sufficient to support both kinds of priming.

Theta oscillations synchronize human medial prefrontal cortex and amygdala during fear learning.

Numerous animal studies have demonstrated that fear acquisition and expression rely on the coordinated activity of medial prefrontal cortex (mPFC) and amygdala and that theta oscillations support interregional communication within the fear network. However, it remains unclear whether these results can be generalized to fear learning in humans. We addressed this question using intracranial electroencephalography recordings in 13 patients with epilepsy during a fear conditioning paradigm. We observed increased power and inter-regional synchronization of amygdala and mPFC in theta (4 to 8 hertz) oscillations for conditioned stimulus (CS+) versus CS-. Analysis of information flow revealed that the dorsal mPFC (dmPFC) led amygdala activity in theta oscillations. Last, a computational model showed that trial-by-trial changes in amygdala theta oscillations predicted the model-based associability (i.e., learning rate). This study provides compelling evidence that theta oscillations within and between amygdala, ventral mPFC, and dmPFC constitute a general mechanism of fear learning across species.

Behavioural and neural evidence for the impact of fluency context on conscious memory.

It has been recently suggested that fluency may impact recognition memory performance when the fluency context varies from trial-to-trial. Surprisingly, such an effect has proved difficult to detect in the masked priming paradigm, one of the most popular means to increase fluency-based memory judgements. We conducted a functional magnetic resonance imaging (fMRI) experiment in which participants encoded words at study and, at test, performed a recognition memory task within a masked priming procedure. In order to optimise the chances of finding priming effects on recognition memory performance, we used low-frequency words, which have been shown to increase hits relative to false alarms and enhance masked priming effects. Fluency context was manipulated by either mixing primed and unprimed trials [Random context (RC) experiment] or blocking primed and unprimed trials [Blocked context (BC) experiment]. Behaviourally, priming affected high-confidence memory performance only in the RC experiment. This behavioural effect correlated positively with neural priming in several recognition memory regions. Moreover, we observed a functional coupling between the left middle temporal gyrus and the left parietal and posterior cingulate cortices that was greater for primed relative to unprimed words. In contrast, in the BC experiment, despite similar activity in recognition-memory-related regions, we did not find any significant correlations between neural and behavioural priming. Finally, we observed striking differences in the neural correlates of masked priming between the RC and BC experiments not only in location but also in direction of the neural response. Possible implications of these findings are discussed.

The pupil as an indicator of unconscious memory: Introducing the pupil priming effect.

We explored whether object behavioral priming and pupil changes occur in the absence of recognition memory. Experiment 1 found behavioral priming for unrecognized objects (Ms) regardless of whether they had been encoded perceptually or conceptually. Using the same perceptual encoding task, Experiment 2 showed greater pupil dilation for Ms than for correct rejections of unstudied objects (CRs) when reaction times were matched. In Experiment 3, there was relatively less pupil dilation for Ms than for similarly matched CRs when objects had been encoded conceptually. Mean/peak pupil dilation for CRs, but not Ms, increased in Experiment 3, in which novelty expectation was also reduced, and the pupillary time course for both Ms and CRs was distinct in the two experiments. These findings indicate that both behavioral and pupil memory occur for studied, but unrecognized stimuli, and suggest that encoding and novelty expectation modulate pupillary memory responses.