Rhinal–hippocampal coupling during declarative memory formation: Dependence on item characteristics (original) (raw)
Related papers
European Journal of Neuroscience, 2003
The hippocampus and the rhinal cortex, two substructures of the medial temporal lobe, together play a crucial role in human declarative memory formation. To investigate in detail the mechanism connecting these two structures transiently during memory formation we recorded depth EEG in epilepsy patients from within the hippocampus and the rhinal cortex. During this recording, patients performed a single-trial word list-learning paradigm with a free recall memory test following a distraction task. Rhinal±hippocampal EEG coherence and spectral power at both locations in the time interval up to 2 s after onset of word presentation were analysed in the frequency range 1±19 Hz. Successful as opposed to unsuccessful memory formation was associated with a general rhinal±hippocampal coherence enhancement, but without alterations in spectral power. Coherence increases in the theta range were correlated with the previously reported memory-related changes in rhinal±hippocampal gamma phase synchronization. This correlation may suggest an interaction of the two mechanisms during declarative memory formation. While theta coherence might be associated with slowly modulated coupling related to an encoding state, rhinal±hippocampal gamma synchronization may be more closely related to actual memory processes by enabling fast coupling and decoupling of the two structures.
Differential contributions of the hippocampus and rhinal cortices to verbal memory in epilepsy
Epilepsy & Behavior, 2007
The present study explored the left mesial temporal lobe correlates of verbal memory in patients with temporal lobe epilepsy (TLE). An index of structural integrity, T2 relaxation time, was measured bilaterally in three mesial temporal regions of interest, and correlated with measures of verbal memory. The acquisition of verbal arbitrary relational material was most strongly associated with left perirhinal T2 signal. In contrast, verbal memory consolidation was related to T2 signal in the left hippocampus. Our findings suggest a key role for the left perirhinal region in the uptake of arbitrary linkages that underlie new learning. The hippocampus, on the other hand, is important for protecting newly learned information from the effects of interference. This double dissociation provides a neurocognitive account of the left mesial temporal memory syndrome.
Human declarative memory formation: Segregating rhinal and hippocampal contributions
Hippocampus, 2002
The medial temporal lobe (MTL) is the core structure of the declarative memory system, but which specific operation is performed by anatomically defined MTL substructures? One hypothesis proposes that the hippocampus carries out an exclusively mnemonic operation during declarative memory formation that is insensitive to content, whereas the rhinal cortex carries out an operation supporting memory formation indirectly. To explore the interaction between a salient item feature and memory formation, we contrasted neural correlates of memory formation of high-and low-frequency words. Event-related potentials (ERPs) were recorded via depth electrodes from within the MTL in nine epilepsy patients while they memorized single words. To assess memory formation, ERPs to words subsequently recalled in a free recall test were contrasted with ERPs to forgotten words. More high-than low-frequency words were remembered. High-frequency words led to distinct ERP subsequent memory effects in rhinal cortex and hippocampus. Low-frequency words, however, were only associated with the hippocampal ERP effect. The anatomically restricted interaction between word frequency and memory formation might indicate a semantically affected operation in the parahippocampal region supporting memory formation indirectly. By contrast, the missing interaction in hippocampal recordings might suggest a direct correlate of declarative memory formation that is insensitive to item properties. Hippocampus 2002;12:514 -519.
2002 Fernandez et al. HIPPOCAMPUS-514-9
The medial temporal lobe (MTL) is the core structure of the declarative memory system, but which specific operation is performed by anatomically defined MTL substructures? One hypothesis proposes that the hippocampus carries out an exclusively mnemonic operation during declarative memory formation that is insensitive to content, whereas the rhinal cortex carries out an operation supporting memory formation indirectly. To explore the interaction between a salient item feature and memory formation, we contrasted neural correlates of memory formation of high-and low-frequency words. Event-related potentials (ERPs) were recorded via depth electrodes from within the MTL in nine epilepsy patients while they memorized single words. To assess memory formation, ERPs to words subsequently recalled in a free recall test were contrasted with ERPs to forgotten words. More high-than low-frequency words were remembered. High-frequency words led to distinct ERP subsequent memory effects in rhinal cortex and hippocampus. Low-frequency words, however, were only associated with the hippocampal ERP effect. The anatomically restricted interaction between word frequency and memory formation might indicate a semantically affected operation in the parahippocampal region supporting memory formation indirectly. By contrast, the missing interaction in hippocampal recordings might suggest a direct correlate of declarative memory formation that is insensitive to item properties. Hippocampus 2002;12:514 -519.
Real-time tracking of memory formation in the human rhinal cortex and hippocampus
Science, 1999
A fundamental question about human memory is which brain structures are involved, and when, in transforming experiences into memories. This experiment sought to identify neural correlates of memory formation with the use of intracerebral electrodes implanted in the brains of patients with temporal lobe epilepsy. Event-related potentials (ERPs) were recorded directly from the medial temporal lobe (MTL) as the patients studied single words. ERPs elicited by words subsequently recalled in a memory test were contrasted with ERPs elicited by unrecalled words. Memory formation was associated with distinct but interrelated ERP differences within the rhinal cortex and the hippocampus, which arose after about 300 and 500 milliseconds, respectively. These findings suggest that declarative memory formation is dissociable into subprocesses and sequentially organized within the MTL.
2003 Fell et al. EUR J NEUROSCI 1082-8
The hippocampus and the rhinal cortex, two substructures of the medial temporal lobe, together play a crucial role in human declarative memory formation. To investigate in detail the mechanism connecting these two structures transiently during memory formation we recorded depth EEG in epilepsy patients from within the hippocampus and the rhinal cortex. During this recording, patients performed a single-trial word list-learning paradigm with a free recall memory test following a distraction task. Rhinal±hippocampal EEG coherence and spectral power at both locations in the time interval up to 2 s after onset of word presentation were analysed in the frequency range 1±19 Hz. Successful as opposed to unsuccessful memory formation was associated with a general rhinal±hippocampal coherence enhancement, but without alterations in spectral power. Coherence increases in the theta range were correlated with the previously reported memory-related changes in rhinal±hippocampal gamma phase synchronization. This correlation may suggest an interaction of the two mechanisms during declarative memory formation. While theta coherence might be associated with slowly modulated coupling related to an encoding state, rhinal±hippocampal gamma synchronization may be more closely related to actual memory processes by enabling fast coupling and decoupling of the two structures.
Hippocampal functional connectivity reflects verbal episodic memory network integrity
NeuroReport, 2007
Using functional magnetic resonance imaging during a verbal memory task, we investigated correlations of signal £uctuations within the hippocampus and ipsilateral frontal as well as temporal areas in temporal lobe epilepsy patients.Declarative memory abilities were additionally examined before and after temporal lobe epilepsy surgery. A signi¢cant di¡erence exists in functional connectivity between patients whose mnemonic functions deteriorated and those who remained stable or improved. Univariate analyses showed signi¢cantly higher preoperative coupling between the hippocampus and Brodmann area 22 for the group that decreased in verbal learning. We suggest greater coupling to re£ect higher functional network integrity. Postoperatively reduced learning ability in patients with higher preoperative coupling underlines the importance of hippocampal interaction with cortical areas for successful memory formation.
Brain : a journal of neurology, 2014
To clarify the anatomical organization of human memory remains a major challenge in clinical neuroscience. Experimental data suggest dentate gyrus granule cells play a major role in memory acquisition, i.e. pattern separation and rapid pattern completion, whereas hippocampal CA1 neurons are implicated in place memory and autobiographical memory retrieval. Patients with temporal lobe epilepsy present with a broad spectrum of memory impairment, which can be assessed during clinical examination. Although long seizure histories may contribute to a pathophysiological reorganization of functional connectivity, surgical resection of the epileptic hippocampus offers a unique possibility to anatomically study the differential contribution of hippocampal subfields to compromised learning and memory in humans. Herein, we tested the hypothesis of hippocampal subfield specialization in a series of 100 consecutive patients with temporal lobe epilepsy submitted to epilepsy surgery. Memory profiles...
Corticothalamic phase synchrony and cross-frequency coupling predict human memory formation
eLife, 2014
The anterior thalamic nucleus (ATN) is thought to play an important role in a brain network involving the hippocampus and neocortex, which enables human memories to be formed. However, its small size and location deep within the brain have impeded direct investigation in humans with non-invasive techniques. Here we provide direct evidence for a functional role for the ATN in memory formation from rare simultaneous human intrathalamic and scalp electroencephalogram (EEG) recordings from eight volunteering patients receiving intrathalamic electrodes implanted for the treatment of epilepsy, demonstrating real-time communication between neocortex and ATN during successful memory encoding. Neocortical-ATN theta oscillatory phase synchrony of local field potentials and neocortical-theta-to-ATN-gamma cross-frequency coupling during presentation of complex photographic scenes predicted later memory for the scenes, demonstrating a key role for the ATN in human memory encoding.