Biology subjects

Kafkas, A.

Publications and source records attributed to Kafkas, A..

5 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↗

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↗

bioRxiv2021

Encoding-linked pupil response is modulated by expected and unexpected novelty: Implications for memory formation and neurotransmission

Whether a novel stimulus is expected or unexpected may have implications for the kind of ensuing encoding and the type of subsequent memory. Pupil response was used in the present study to explore the way expected and unexpected stimuli are encoded and whether encoding-linked pupil response is modulated by expectation. Participants first established a contingency relationship between a series of symbols and the type of stimulus (man-made or natural) that followed each one. At encoding, some of the target stimuli violated the previously established relationship (i.e., unexpected), while the majority conformed to this relationship (i.e., expected). Expectation at encoding had opposite effects on familiarity and recollection, the two types of memory that support recognition, and modulated differently the way pupil responses predicted subsequent memory. Encoding of unexpected novel stimuli was associated with increased pupil dilation as a predictor of subsequent memory type and strength. In contrast, encoding of expected novel stimuli was associated with decreased pupil response (constriction), which was predictive of subsequent memory type and strength. The findings support the close link between pupil response and memory formation, but critically indicate that this is modulated by the type of novelty as defined by expectation. These novel findings have important implications for the encoding mechanisms involved when different types of novelty are detected and is proposed to indicate the operation of different neurotransmitters in memory formation.

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↗