Dynamic shaping of memory representations by physiological and cognitive processes
Freitag, 04.06.2021:
13:00 - 14:30

Chair der Sitzung: Svenja Brodt, Universität Tübingen
Chair der Sitzung: Monika Schönauer, University of Freiburg
Ort: Learning, memory, and sleep

Zusammenfassung der Sitzung

Not only do our memories shape how we perceive and interact with the world, they themselves are influenced by many factors, both internal and external. Innovative experimental designs, analysis approaches and human neuroimaging methods allow us to investigate the dynamics of how memory representations evolve and change in bilateral interaction with other cognitive and physiological processes. In this symposium, we present data from five labs, each focusing on different modulators of internal representations. We will first highlight physiological determinants of hippocampal function in ageing, based on data from various neuroimaging modalities. To these ends, we will show how differences in hippocampal vascularization patterns impact memory and cognitive functioning. Moreover, we will present data showing that Alzheimer’s disease pathology differentially affects object and scene memory. Secondly, we will discuss how episodic simulation can shape real-life attitudes: mentally associating existing memory representations can lead to a transfer of affective valence to a previously neutral stimulus, resulting in both behavioral and physiological changes. Finally, we will focus on cognitive factors that support the emergence of neocortical memory representations. A first contribution leverages multivariate pattern analysis to show how the neocortex is able to rapidly acquire content-specific representations through repeated rehearsal. We will also present data on how sleep supports neocortical memory formation by shifting subcortical contributions to mnemonic processing during retrieval.


Hippocampal vascularization as a potential reserve factor

Niklas Vockert

Deutsches Zentrum für Neurodegenerative Erkrankungen

The hippocampus within the medial temporal lobe (MTL) is highly vulnerable to age-related pathology such as vascular disease. Technical advances in MRI recently enabled the visualization of hippocampal blood vessels at an unprecedented resolution, permitting the classification of hippocampal vascularization patterns (HVP) in vivo. Dual-supply hemispheres with a contribution of the anterior choroidal artery to hippocampal blood supply can be distinguished from single-supply ones with a sole dependence on the posterior cerebral artery. In an older cohort of 47 patients with cerebral small vessel disease and controls, a dual vascular supply was positively associated with measures of cognition and brain structure. Notably, structural differences associated with the HVP were observed specifically in the anterior MTL, but also in relation to total grey matter volumes, indicating that the HVP has more far-reaching structural implications beyond the MTL. Hence, an augmented hippocampal vascularization might contribute to maintaining structural integrity in the brain and preserving cognition despite age-related degeneration.

Anterior medial temporal lobe networks and memory for objects are affected in early stages of Alzheimer's disease

David Berron

Deutsches Zentrum für Neurodegenerative Erkrankungen, Deutschland

Memory networks in the human medial temporal lobe and the neocortex support different types of memory. On the other hand, Alzheimer’s disease pathology affects these memory networks differentially in early disease stages. This holds the promise to identify cognitive markers for early identification of Alzheimer’s disease related memory impairment. I will show data demonstrating that tau neurofibrillary tangle pathology predominantly affects brain regions in the anterior medial temporal lobe that have been reported to support critical memory functions. Using functional magnetic resonance imaging and a memory paradigm comparing memory for objects and scenes, I will show that brain regions that are primarily involved in memory for objects overlap with the spatial distribution of early tau pathology in AD and show aberrant activity in healthy ageing. Finally, I will show that in particular memory performance for objects, but not scenes, is associated with measures of tau pathology in patients with preclinical Alzheimer’s disease. This work suggests that cognitive measures targeting mnemonic functions related to the anterior medial temporal lobe might be particularly suitable to detect the earliest cognitive impairment in Alzheimer’s disease.

Simulation-induced learning: Episodic simulations shape real-life attitudes

Philipp C. Paulus1,2, Aroma Dabas1, Annalena Felber1, Roland G. Benoit1

1Max Planck Research Group: Adaptive Memory, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany; 2International Max Planck Research School NeuroCom, Leipzig, Germany

Humans can vividly simulate prospective episodes. This ability draws on our existing knowledge (e.g., of people and locations) to create an imaginary parallel to actual experience (e.g., of meeting a person at a location). Recent evidence suggests that we learn from such simulated experiences much as from actual experiences. In an initial study, we showed that merely simulating familiar people (serving as unconditioned stimuli; UCS) at known locations (conditioned stimuli; CS) changes people’s attitudes towards the locations. Here, we further test the hypothesis that such simulation-based learning entails a merging of the representations of the UCS and CS and thus a transfer of value from the UCS to the CS. Consistent with this account, we first show that (i) repeated simulations strengthen the associations between the paired CS and UCS and that (ii) – compared to a neutral baseline – positive UCS lead to an upward shift and negative UCS to a downward shift in people’s attitude towards the respective CS. Notably, simulations featuring liked and disliked people were characterized by increased levels of skin conductance and the transfer of value can be accounted for by the affective experience during the simulations. The data thus support the hypothesis that we can learn from affective episodic simulations much as we learn from actual experience.

The neocortex rapidly acquires a content-specific representation of naturalistic learning material

Katja Kleespies1, Madeleine W. Sumner2, Elizabeth A. McDevitt2, Christopher Baldassano3, Uri Hasson2, Kenneth A. Norman2, Monika Schönauer1

1Albert-Ludwigs-Universität Freiburg, Deutschland; 2Princeton University, Princeton, NJ, USA; 3Columbia University, New York, USA

Traditional theories of long-term memory formation assume that the neural traces which encode new memories are rapidly formed in the hippocampus and then slowly shifted to the neocortex, where acquired memory contents become integrated and semanticized over the course of weeks or months. However, recent studies emphasize the importance of neocortical areas such as posterior medial cortex (PMC) or medial prefrontal cortex already early in memory formation. We tested whether the neocortex not only functionally contributes to encoding and retrieval, but also quickly represents the specific content of learning material when participants engage with new and complex naturalistic stimuli. Participants (𝑁=40) encoded and freely recalled audio-visual movies depicting either restaurant or airport scenes. They repeated this multiple times while their brain activity was measured with functional magnetic resonance imaging. Using multivariate pattern analyses, we identified brain regions involved in the learning and retrieval of the movie material by representing the content of the narratives. Here, a comparison of the similarity of neural activation patterns within and between movies set in restaurants or airports revealed that only in the PMC and inferior parietal lobule, patterns within movie conditions were more similar than between movie conditions. Because movie content could be reliably separated in the parietal cortex, we suggest that it harbors a memory trace. Together with other recent studies on rapidly formed engrams in the parietal cortex, our results challenge traditional assumptions on long-term memory formation. The neocortex can acquire complex, content-specific memory representations already early in the learning process.

Sleep benefits memory retention by stabilizing functional activity and enhancing hippocampal independence in the posterior medial memory network, thalamus and striatum

Svenja Brodt

Universität Tübingen, Deutschland

Sleep has robustly been shown to benefit declarative memory consolidation on a behavioral level, the underlying mechanisms in terms of functional activation of mnemonic brain networks however remain unclear. While most report an increase in cortical activation across sleep, results on subcortical involvement diverge (Gais et al 2007; Himmer et al 2019; Takashima et al 2009). Here, we aimed to assess the role of sleep on memory-related brain activity in cortical and subcortical networks.

Participants repeatedly learned object-place associations in two sessions spaced 13 hours apart. The wake group (n=19) encountered task session 1 in the morning, spent the day awake and returned for session 2 in the evening. The sleep group (n=20) completed session 1 in the evening, slept at home with mobile polysomnography and returned the next morning. Task-related functional brain activity was recorded via fMRI.

Behaviorally, sleep benefitted memory retention. This effect was accompanied by a stabilization/decrease of functional brain activity during recall across sleep/wake in the precuneus, striatum and thalamus. Upregulation of activity in these areas was associated with behavioral benefits. Furthermore, the three regions displayed reduced connectivity to the hippocampus specifically across sleep, with lower hippocampal connectivity of the thalamus and striatum relating to better memory performance in addition to the effect of activation increase.

Together, our analyses show that sleep might benefit memory retention by stabilizing memory-related brain activity and increasing hippocampal independence of a mnemonic network encompassing posterior medial cortex as well as subcortical regions like the thalamus and striatum.