Biology subjects

Montaldi, D.

Publications and source records attributed to Montaldi, D..

7 recordsLinked to original sources

bioRxiv2026

Hippocampal-midbrain interactions link encoding-related pupil response to memory success

Encoding-related pupil responses predict later memory performance, but the neural mechanisms linking these autonomic dynamics to memory formation remain unclear. This study examined whether pupil responses during encoding track activity in the brains memory network and whether they reflect functional interactions between memory-related regions and neural systems involved in pupil control. Participants performed an incidental encoding task involving object stimuli while undergoing simultaneous fMRI and pupillometry; recognition memory was subsequently assessed outside the scanner. Greater pupil constriction during encoding predicted both the strength and quality of later memory. These pupil dynamics correlated with activity in memory-related brain regions, notably the hippocampus and the parahippocampal cortex. Connectivity analyses indicated that encoding-related pupil responses were supported by functional interactions between the hippocampus and the midbrain Edinger-Westphal nucleus, the striatum, and the orbitofrontal cortex. The findings suggest that interactions between memory-related regions and parasympathetic pupil-control systems may modulate encoding efficiency. Together, the results identify encoding-related pupil constriction as a non-invasive marker of memory-network engagement and suggest a hippocampal-midbrain pathway through which autonomic pupil dynamics are coupled with successful memory formation.

neuroscience↗

bioRxiv2024

Cerebrovascular Health Mediates Processing Speed Change Through Anterior White Matter Alterations: A UK Biobank Study

Cerebrovascular disease is associated with an increased likelihood of developing dementia. While cardiovascular risk factors are modifiable and may reduce the risk of later-life cognitive dysfunction, the relationship between cerebrovascular risk factors, brain integrity and cognition remains poorly characterised. Using a large UK Biobank sample of predominantly middle-aged adults, without neurological disease, our structural equation mediation models showed that poor cerebrovascular health, indicated by the presence of cerebrovascular risk factors, was associated with slowed processing speed. This effect was best explained by anterior white matter microstructure changes, rather than posterior changes. Effects were also significantly reduced when considering other forms of cognition, demonstrating both regional- and cognitive-specificity of our effects. Critically, our findings also demonstrate that including measures of risk factor duration may be particularly important for improving estimations of cerebrovascular burden. In summary, our study demonstrates the specific impact of early cerebrovascular burden on brain structure and cognitive function, highlighting the necessary next steps for improving cerebrovascular burden quantification and improving clinical predictions.

neuroscience↗

bioRxiv2023

The hippocampus assumes a special role in supporting abstract concept representation

Unlike images, words are representational symbols. The associative details inherent within a words meaning and the visual imagery it generates, are inextricably connected to the way words are processed and represented. It is well recognised that the hippocampus associatively binds components of a memory to form a lasting representation, and here we show that the hippocampus is especially sensitive to abstract word processing. Using fMRI during recognition we found that the increased abstractness of words produced increased hippocampal activation and that critically this was independent of memory. Interestingly, word recollection produced hippocampal activation independent of word abstractness, while the parahippocampal cortex was sensitive to concrete word representation, independent of memory. We reason that the hippocampus has assumed a critical role in the representation of uncontextualized abstract word meaning, as its information-binding ability allows the retrieval of the semantic and visual associates that, when bound together, generate the abstract concept represented by word symbols. These novel findings not only offer insights for research drawing on word representation, memory, and hippocampal integrity, but critically, they throw important light on how the human brain may have adapted to encode and represent abstract words and concepts as they emerged in our language.

neuroscience↗

bioRxiv2020

Expectation violation dynamically engages a bottom-up encoding state

To efficiently process information, the brain shifts between encoding and retrieval states, prioritising bottom-up or top-down processing accordingly. Expectation violation before or during learning has been shown to trigger an adaptive encoding mechanism, resulting in better memory for unexpected events. Using fMRI we explored (1) whether this encoding mechanism is also triggered during retrieval, and if so, (2) what the temporal dynamics of its mnemonic consequences are. Male and female participants studied object images, then, with new objects, they learned a contingency between a cue and a semantic category. Rule-abiding (expected) and violating (unexpected) targets and similar foils were used at test. We found interactions between previous and current similar events expectation, such that when an expected event followed a similar but unexpected event, its performance was boosted, underpinned by activation in the hippocampus, midbrain, and occipital cortex. In contrast, a sequence of two unexpected similar events also triggered occipital engagement, however, this did not enhance memory performance. Taken together, our findings suggest that when the goal is to retrieve, encountering surprising events engages an encoding mechanism, supported by bottom-up processing, that may enhance memory for future related events. Significance statementOptimising the balance between new learning and the retrieval of existing knowledge is an ongoing process, at the core of human cognition. Previous research into memory encoding suggests experiencing surprise leads to the prioritisation of the leaning of new memories, forming an adaptive encoding mechanism. We examined whether this mechanism is also engaged when the current goal is to retrieve information. Our results demonstrate that an expectation-driven shift towards an encoding state, supported by enhanced perceptual processing, is beneficial for the correct identification of subsequent expected similar events. These findings have important implications for our understanding of the temporal dynamics of the adaptive encoding of information into memory.

neuroscience↗

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↗