Biology subjects

Montaldi, D.

Publications and source records attributed to Montaldi, D..

3 recordsLinked to original sources

bioRxiv2019

Thalamic-medial temporal lobe connectivity underpins familiarity memory

The neural basis of memory is highly distributed, but the thalamus is known to play a particularly critical role. However, exactly how the different thalamic nuclei contribute to different kinds of memory is unclear. Moreover, whether thalamic connectivity with the medial temporal lobe (MTL), arguably the most fundamental memory structure, is critical for memory, remains unknown. We explore these questions using an fMRI recognition memory paradigm that taps familiarity and recollection (i.e., the two types of memory that support recognition) for objects, faces and scenes. We show that the mediodorsal thalamus (MDt) plays a material-general role in familiarity, while the anterior thalamus plays a material-general role in recollection. Material-specific regions were found for scene familiarity (ventral posteromedial and pulvinar thalamic nuclei) and face familiarity (left ventrolateral thalamus). Critically, increased functional connectivity between the MDt and the parahippocampal (PHC) and perirhinal cortices (PRC) of the MTL underpinned increases in reported familiarity confidence. These findings suggest that familiarity signals are generated through the dynamic interaction of functionally connected MTL-thalamic structures.

neuroscience↗

bioRxiv2019

Computational modelling of hippocampal sensitivity to expectation violation

Pattern separation and completion are fundamental hippocampal computations supporting memory encoding and retrieval. However, despite extensive exploration of these processes, it remains unclear whether they are modulated by top-down processes. We used a neural network model to examine how unexpected information is represented by the hippocampus. During training the network learned a contingency between a cue and a category, which the target object belongs to. At test, we presented the network with congruous and incongruous cues, as well as perceptually similar foils. We used representational similarity analysis to examine how the top-down expectation modulation interacts with bottom-up perceptual input, in each layer. All subfields showed an interaction between the two, with DG and CA3 being more sensitive to expectation violation than CA1. A further multivariate analysis revealed that representational differences between expected and unexpected inputs were prominent for moderate to high levels of perceptual overlap in DG/CA3. This effect diminished when inputs from DG and CA3 into CA1 were lesioned. Overall, our findings suggest pattern separation in DG and CA3 underlies the effect that violation of expectation exerts on memory.

neuroscience↗

bioRxiv2019

Pattern separation is the key driver of expectation-modulated memory

The hippocampus uses pattern separation and pattern completion in a continuous manner to successfully encode and retrieve memories1,2. However, whether and how cognitive factors might modulate the dynamics between these types of computation is not well understood. Here we examine the role of expectation in shifting the hippocampus to perform pattern separation. Expectation can be built up through multiple contextual exposures leading to prediction (as in a learnt contingency) or through logical deduction based on a previous mnemonic response. Participants first learned a contingency between a cue and an objects category (man-made or natural). Then, at encoding, one third of the cues that preceded the to-be-memorised objects violated the studied rule. At test, participants performed an old/new recognition task with old items (targets) and a set of parametrically manipulated (very similar to dissimilar) new foils for each object. We explored the effects of both contextual expectation, manipulated at initial encoding, and mnemonic-attribution expectation, driven by the mnemonic decisions taken on previous retrieval trials. For example, a target would be unexpected if in a previous trial a similar foil had been erroneously accepted as old. Memory was found to be better for foils of high and mid similarity to contextually unexpected targets at encoding, compared to expected ones. Additionally, violations of mnemonic-attribution expectation also yielded improved memory performance when the level of foil similarity was high. These results suggest that violations of both contextual expectation and mnemonic-attribution expectation engage pattern separation, resulting in better discrimination performance for these items. Importantly, this mechanism is engaged when input differentiation is required in order to make a correct recognition decision.

neuroscience↗