Time and memory distrust shape the dynamics of recollection and belief-in-occurrence The current study examined how people’s metamemory judgments of recollection and belief-in-occurrence change over time. Furthermore, we examined to what extent these judgments are affected by memory distrust – the subjective appraisal of one’s memory functioning – as measured by the Memory Distrust Scale (MDS) and the Squire Subjective Memory Scale (SSMQ). Participants (N = 234) studied pictorial stimuli and were tested on some of these stimuli later in the same session, but were tested on other stimuli 1, 2, 4, 8, and 17 days later. Recollection and belief ratings were correlated highly and followed similar declining patterns over time. However, belief decreased relatively more slowly than recollection, such that the discrepancy between recollection and belief increased over time. Memory distrust moderated the association between recollection and belief, with this association being weaker among people who reported greater (versus lower) memory distrust. Memory distrust also interacted with retention period to predict memory judgments. Two measures of memory distrust diverged in their predictive power. In particular, only the MDS predicted the spontaneous reporting of nonbelieved memories. Our results provide support to the theoretical perspective that belief-in-occurrence is a summative judgment informed not only by recollective phenomenology but also by metamemorial beliefs.
A scalable spiking amygdala model that explains fear conditioning, extinction, renewal and generalization The amygdala (AMY) is widely implicated in fear learning and fear behaviour, but it remains unclear how the many biological components present within AMY interact to achieve these abilities. Building on previous work, we hypothesize that individual AMY nuclei represent different quantities and that fear conditioning arises from error-driven learning on the synapses between AMY nuclei. We present a computational model of AMY that (a) recreates the divisions and connections between AMY nuclei and their constituent pyramidal and inhibitory neurons; (b) accommodates scalable high-dimensional representations of external stimuli; (c) learns to associate complex stimuli with the presence (or absence) of an aversive stimulus; (d) preserves feature information when mapping inputs to salience estimates, such that these estimates generalize to similar stimuli; and (e) induces a diverse profile of neural responses within each nucleus. Our model predicts (1) defensive responses and neural activities in several experimental conditions, (2) the consequence of artificially ablating particular nuclei and (3) the tendency to generalize defensive responses to novel stimuli. We test these predictions by comparing model outputs to neural and behavioural data from animals and humans. Despite the relative simplicity of our model, we find significant overlap between simulated and empirical data, which supports our claim that the model captures many of the neural mechanisms that support fear conditioning. We conclude by comparing our model to other computational models and by characterizing the theoretical relationship between pattern separation and fear generalization in healthy versus anxious individuals.
Egocentric and Allocentric Spatial Memory for Body Parts: a Virtual Reality Study Extensive literature elucidated the mechanisms underlying the ability to memorize the positions of objects in space. However, less is known about the impact that objects’ features have on spatial memory. The present study aims to investigate differences in egocentric and allocentric object-location memory between hand stimuli depicted in a first-person perspective (1PP) or in a third-person one (3PP). Fifty-two adults encoded spatial positions within a virtual museum environment featuring four square buildings. Each of these buildings featured eight paintings positioned along the walls, with two pictures displayed on each of the four walls. Thirty-two stimuli were employed, which represented pictures of the right hand performing various types of gestures. Half of the stimuli depicted the hand in the 1PP, while the other half depicted the hand in the 3PP. Both free and guided explorations served as encoding conditions. Immediately after that, participants underwent a two-step object-location memory task. Participants were provided with a map of the museum and asked to identify the correct building where the image was located (allocentric memory). Then, they were presented with a schematic representation of the exhibition room divided into four sections and instructed to select the section where they thought the picture was located (egocentric memory). Our findings indicate a memory performance boost associated with egocentric recall, regardless of the perspective of the bodily stimuli. The results are discussed considering the emerging literature on the mnemonic properties of body-related stimuli for spatial memory.
Modulation of perceived motion by illusory contours, and the rigidity assumption Here we present demonstrations that combine illusory edge motion with Kanizsa figures. The key observation is that even though each local edge of a Kanizsa square signals a vertical or horizontal shift, the global percept is that of rotation. The conflict between the global percept and local motion information is at odds with the observers’ assumption that the perceived figure is rigid and unlikely to deform. The local/global conflict creates a bistable percept that allows an exploration of the relationships between perceptual modes. Variants of the original figure were created to identify and assess critical factors of this phenomenon, including changes in temporal phase and amodal completion of motion.
Oscillatory Coupling Between Neural and Cardiac Rhythms Oscillations serve a critical role in organizing biological systems. In the brain, oscillatory coupling is a fundamental mechanism of communication. The possibility that neural oscillations interact directly with slower physiological rhythms (e.g., heart rate, respiration) is largely unexplored and may have important implications for psychological functioning. Oscillations in heart rate, an aspect of heart rate variability (HRV), show remarkably robust associations with psychological health. Mather and Thayer proposed coupling between high-frequency HRV (HF-HRV) and neural oscillations as a mechanism that partially accounts for such relationships. We tested this hypothesis by measuring phase-amplitude coupling between HF-HRV and neural oscillations in 37 healthy adults at rest. Robust coupling was detected in all frequency bands. Granger causality analyses indicated stronger heart-to-brain than brain-to-heart effects in all frequency bands except gamma. These findings suggest that cardiac rhythms play a causal role in modulating neural oscillations, which may have important implications for mental health.
Stereo-EEG features of temporal and frontal lobe seizures with loss of consciousness The loss of consciousness (LOC) during seizures is one of the most striking features that significantly impact the quality of life, even though the neuronal network involved is not fully comprehended. We analyzed the intracerebral patterns in patients with focal drug-resistant epilepsy, both with and without LOC. We assessed the localization, lateralization, stereo electroencephalography (SEEG) patterns, seizure duration, and the quantification of contacts exhibiting electrical discharge. The degree of LOC was quantified using the Consciousness Seizure Scale. Thirteen patients (40 seizures) with focal drug-resistant epilepsy underwent SEEG. In cases of temporal lobe epilepsy (TLE, 6 patients and 15 seizures), LOC occurred more frequently in seizures with mesial rather than lateral temporal lobe onset. On the other hand, in cases of frontal lobe epilepsy (7 patients; 25 seizures), LOC was associated with pre-frontal onset, a higher number of contacts with epileptic discharge compared to the onset count and longer seizure durations. Our study revealed distinct characteristics during LOC depending on the epileptogenic zone. For temporal lobe seizures, LOC was associated with mesial seizure onset, whereas in frontal lobe epilepsy, seizure with LOC has a significant increase in contact showing epileptiform discharge and a pre-frontal onset. This phenomenon may be correlated with the broad neural network required to maintain consciousness, which can be affected in different ways, resulting in LOC
Brain-derived neurotrophic factor scales presynaptic calcium transients to modulate excitatory neurotransmission Brain-derived neurotrophic factor (BDNF) plays a critical role in synaptic physiology, as well as mechanisms underlying various neuropsychiatric diseases and their treatment. Despite its clear physiological role and disease relevance, BDNF’s function at the presynaptic terminal, a fundamental unit of neurotransmission, remains poorly understood. In this study, we evaluated single synapse dynamics using optical imaging techniques in hippocampal cell cultures. We find that exogenous BDNF selectively increases evoked excitatory neurotransmission without affecting spontaneous neurotransmission. However, acutely blocking endogenous BDNF has no effect on evoked or spontaneous release, demonstrating that different approaches to studying BDNF may yield different results. When we suppressed BDNF-Tropomyosin receptor kinase B (TrkB) activity chronically over a period of days to weeks using a mouse line enabling conditional knockout of TrkB, we found that evoked glutamate release was significantly decreased while spontaneous release remained unchanged. Moreover, chronic blockade of BDNF-TrkB activity selectively downscales evoked calcium transients without affecting spontaneous calcium events. Via pharmacological blockade by voltage-gated calcium channel (VGCC) selective blockers, we found that the changes in evoked calcium transients are mediated by the P/Q subtype of VGCCs. These results suggest that BDNF-TrkB activity increases presynaptic VGCC activity to selectively increase evoked glutamate release.
Zona incerta modulation of the inferior olive and the pontin The zona incerta (ZI) is a subthalamic structure that has been implicated in locomotion, fear, and anxiety. Recently interest has grown in its therapeutic efficacy in deep brain stimulation in movement disorders. This efficacy might be due to the ZI’s functional projections to the other brain regions. Notwithstanding some evidence of anatomical connections between the ZI and the inferior olive (IO) and the pontine nuclei (PN), how the ZI modulates the neuronal activity in these regions remains to be determined. We first tested this by monitoring responses of single neurons in the PN and IO to optogenetic activation of channelrhodopsin-expressing ZI axons in wild-type mice, using an in vivo awake preparation. Stimulation of short, single pulses and trains of stimuli at 20 Hz elicited rapid responses in the majority of recorded cells in the PN and IO. Furthermore, the excitatory response of PN neurons scaled with the strength of ZI activation. Next, we used in vitro electrophysiology to study synaptic transmission at ZI-IO synapses. Optogenetic activation of ZI axons evoked a strong excitatory postsynaptic response in IO neurons, which remained robust with repeated stimulation at 20 Hz. Overall, our results demonstrate a functional connection within ZI-PN and ZI-IO pathways.