Neurocognitive Perspective of Transient Global Amnesia

Transient global amnesia (TGA) is a neuropsychological syndrome that involves a sudden and temporary episode of memory loss that includes inability to create new memories. It has been shown that this disorder is related with a transitory deficit of the hippocampus function. In this chapter, the preserved and impaired memory pattern of TGA patients will be discussed considering the classical memory systems model. The analysis of this perspective leads to some contradictory or unresolved issues. In order to try to resolve these inconsistencies and considering that TGA is associated with hippocampal perturbation, new research about the hippocampus is analyzed. This new perspective focused on the hippocampal function provides a deeper understanding of the memory loss pattern associated with TGA, and it points out new questions that are not studied yet in the TGA population

Dejä vu and Recognition Memory in Temporal Lobe Epilepsy

Déjà vu is a uniquely curious experience with which many of us are familiar. The experience can be so transient and unpredictable that it typically subsides, just as quickly as it appeared, before one can engage in any meaningful introspective evaluation. At the core of the experience is an impression of familiarity that co-exists with the feeling that it is inappropriate. Currently, there is no consensus among researchers about which theory can best account for the cognitive and neural mechanisms that underlie the experience. The goal of the current study was to examine déjà vu in temporal-lobe epilepsy (TLE) within the framework of the cognitive dual process-model of recognition memory that distinguishes between familiarity and recollection. It was reasoned that TLE patients with déjà vu should also experience deficits in recognition memory inter-ictally and that the exact nature of these deficits might offer insight into the cognitive mechanisms underlying the pathological, subjective experience of déjà vu associated with their seizures. The particular hypothesis tested was that the memory impairments in TLE patients with déjà vu are selective or most pronounced in the domain of familiarity assessment. Toward this end, two experimental recognition memory tasks derived from the cognitive neuroscience literature were administered to patients with unilateral or bilateral seizure origin. In general, converging evidence from the two tasks administered suggests that unilateral TLE patients with déjà vu do indeed have selective familiarity impairments and intact recollection. However, in bilateral cases deficits were found to be broader and included impairments in recollection as well. Inaccurate feelings of familiarity may represent the functional consequence of seizure activity in a region of the MTL critical for assessing feelings of familiarity. Further, these data hint that the cognitive process responsible for identifying the inappropriateness of the sense of familiarity during déjà vu may not be recollection, as previously suggested in the literature. Together, the present findings suggest that probing the cognitive correlates of déjà vu in TLE inter-ictally can advance our understanding of mechanisms involved in déjà vu at a time when experimental paradigms to elicit the experience in the cognitive laboratory are still missing

Rapid presentation rate negatively impacts the contiguity effect in free recall

It is well-known that in free recall participants tend to recall words presented close together in time in sequence, reflecting a form of temporal binding in memory. This contiguity effect is robust, having been observed across many different experimental manipulations. In order to explore a potential boundary on the contiguity effect, participants performed a free recall task in which items were presented at rates ranging from 2 Hz to 8 Hz. Participants were still able to recall items even at the fastest presentation rate, though accuracy decreased. Importantly, the contiguity effect flattened as presentation rates increased. These findings illuminate possible constraints on the temporal encoding of episodic memories.http://sites.bu.edu/tcn/files/2019/05/RSVP_FR.pdfAccepted manuscrip

Mental time in amnesia: evidence from bilateral medial temporal damage before and after recovery

The human mind is continuously involved in "projecting" the self in time in order to process past memories and predict future occurrences. "Self-projection" in time involves episodic and spatial memory, relying on medial-temporal structures, but also engages visuo-spatial imagery, relying on occipito-temporal structures, and self-location, relying on temporo-parietal structures. Here we had the rare opportunity to investigate the relation between self-projection in time and memory, using a novel behavioural paradigm, in a patient with subacute bilateral medial-temporal damage during a period of amnesia as well as after recovery. Despite her memory deficit the patient was able to "project" herself to past and future, yet with significant improvement after recovery. We discuss our findings with respect to the relations between episodic memory and medial-temporal structures with self-projection in time to past and future

Antibody-associated epilepsies: Clinical features, evidence for immunotherapies and future research questions.

PURPOSE: The growing recognition of epilepsies and encephalopathies associated with autoantibodies against surface neuronal proteins (LGI1, NMDAR, CASPR2, GABABR, and AMPAR) means that epileptologists are increasingly asking questions about mechanisms of antibody-mediated epileptogenesis, and about the use of immunotherapies. This review summarizes clinical and paraclinical observations related to autoimmune epilepsies, examines the current evidence for the effectiveness of immunotherapy, and makes epilepsy-specific recommendations for future research. METHOD: Systematic literature search with summary and review of the identified publications. Studies describing the clinical characteristics of autoantibody-associated epilepsies and treatments are detailed in tables. RESULTS: Literature describing the clinical manifestations and treatment of autoimmune epilepsies associated with neuronal cell-surface autoantibodies (NSAbs) is largely limited to retrospective case series. We systematically summarize the features of particular interest to epileptologists dividing patients into those with acute or subacute encephalopathies associated with epilepsy, and those with chronic epilepsy without encephalopathy. Available observational studies suggest that immunotherapies are effective in some clinical circumstances but outcome data collection methods require greater standardization. CONCLUSIONS: The clinical experience captured suggests that clusters of clinical features associate well with specific NSAbs. Intensive and early immunotherapy is indicated when patients present with autoantibody-associated encephalopathies. It remains unclear how patients with chronic epilepsy and the same autoantibodies should be assessed and treated. Tables in this paper provide a comprehensive resource for systematic descriptions of both clinical features and treatments, and highlight limitations of current studies

Neural processes underpinning episodic memory

Episodic memory is the memory for our personal past experiences. Although numerous functional magnetic resonance imaging (fMRI) studies investigating its neural basis have revealed a consistent and distributed network of associated brain regions, surprisingly little is known about the contributions individual brain areas make to the recollective experience. In this thesis I address this fundamental issue by employing a range of different experimental techniques including neuropsychological testing, virtual reality environments, whole brain and high spatial resolution fMRI, and multivariate pattern analysis. Episodic memory recall is widely agreed to be a reconstructive process, one that is known to be critically reliant on the hippocampus. I therefore hypothesised that the same neural machinery responsible for reconstruction might also support ‘constructive’ cognitive functions such as imagination. To test this proposal, patients with focal damage to the hippocampus bilaterally were asked to imagine new experiences and were found to be impaired relative to matched control participants. Moreover, driving this deficit was a lack of spatial coherence in their imagined experiences, pointing to a role for the hippocampus in binding together the disparate elements of a scene. A subsequent fMRI study involving healthy participants compared the recall of real memories with the construction of imaginary memories. This revealed a fronto-temporo-parietal network in common to both tasks that included the hippocampus, ventromedial prefrontal, retrosplenial and parietal cortices. Based on these results I advanced the notion that this network might support the process of ‘scene construction’, defined as the generation and maintenance of a complex and coherent spatial context. Furthermore, I argued that this scene construction network might underpin other important cognitive functions besides episodic memory and imagination, such as navigation and thinking about the future. It is has been proposed that spatial context may act as the scaffold around which episodic memories are built. Given the hippocampus appears to play a critical role in imagination by supporting the creation of a rich coherent spatial scene, I sought to explore the nature of this hippocampal spatial code in a novel way. By combining high spatial resolution fMRI with multivariate pattern analysis techniques it proved possible to accurately determine where a subject was located in a virtual reality environment based solely on the pattern of activity across hippocampal voxels. For this to have been possible, the hippocampal population code must be large and non-uniform. I then extended these techniques to the domain of episodic memory by showing that individual memories could be accurately decoded from the pattern of activity across hippocampal voxels, thus identifying individual memory traces. I consider these findings together with other recent advances in the episodic memory field, and present a new perspective on the role of the hippocampus in episodic recollection. I discuss how this new (and preliminary) framework compares with current prevailing theories of hippocampal function, and suggest how it might account for some previously contradictory data

Assessment of Verbal and Nonverbal Memory and Learning in Abstinent Alcoholics

Neuropsychological performance was measured in chronic alcoholics who maintained abstinence for at least six months and with matched controls. Specifically, measures of verbal memory were assessed utilizing the Rey Auditory Verbal Learning Test (RAVLT) and measures of nonverbal memory with the Rey Osterreith Complex Figure Test (ROCF) and a new measure, the Poreh Nonverbal Memory Test (PNMT). In addition, both the RAVLT and the PNMT provide a measure of operationalized learning, as they are multi-trial tasks utilizing five trials to assess recall in each trial. Verbal memory includes the ability to encode, store and retrieve information for words, language and verbal stimuli. Nonverbal memory reflects the ability to encode, store and retrieve information that is visual and spatial in nature. It is devoid of verbal components and includes abstract designs or nonsense figures. Currently, there are questions as to the validity of many nonverbal memory measures because they allow for sub-vocalization of the tasks thereby utilizing verbal mediation (Wisniewski, Wendling, Manning & Steinhoff, 2012). The present study assessed for differences in verbal and nonverbal memory in abstinent alcoholics and predicted that they would perform more poorly on nonverbal measures while verbal memory would remain intact. Additionally, a comparison of learning curves was examined for each group. Finally, the PNMT was validated by correlating with a current neuropsychological assessment of memory and learning, the RAVLT, and a nonverbal neuropsychological assessment, the ROCF. Results indicated that the abstinent alcoholics differed significantly in nonverbal measurements depending upon the complexity of the tasks. Concerning verbal tasks, there was no significant difference in results across the groups. However, the length of alcohol dependence did significantly predict performance on the RAVLT recognition task indicating possible frontal lobe deficits and disordered recall. Correlational analyses indicate that the utilit

Assessment of Verbal and Nonverbal Memory and Learning in Abstinent Alcoholics

Neuropsychological performance was measured in chronic alcoholics who maintained abstinence for at least six months and with matched controls. Specifically, measures of verbal memory were assessed utilizing the Rey Auditory Verbal Learning Test (RAVLT) and measures of nonverbal memory with the Rey Osterreith Complex Figure Test (ROCF) and a new measure, the Poreh Nonverbal Memory Test (PNMT). In addition, both the RAVLT and the PNMT provide a measure of operationalized learning, as they are multi-trial tasks utilizing five trials to assess recall in each trial. Verbal memory includes the ability to encode, store and retrieve information for words, language and verbal stimuli. Nonverbal memory reflects the ability to encode, store and retrieve information that is visual and spatial in nature. It is devoid of verbal components and includes abstract designs or nonsense figures. Currently, there are questions as to the validity of many nonverbal memory measures because they allow for sub-vocalization of the tasks thereby utilizing verbal mediation (Wisniewski, Wendling, Manning & Steinhoff, 2012). The present study assessed for differences in verbal and nonverbal memory in abstinent alcoholics and predicted that they would perform more poorly on nonverbal measures while verbal memory would remain intact. Additionally, a comparison of learning curves was examined for each group. Finally, the PNMT was validated by correlating with a current neuropsychological assessment of memory and learning, the RAVLT, and a nonverbal neuropsychological assessment, the ROCF. Results indicated that the abstinent alcoholics differed significantly in nonverbal measurements depending upon the complexity of the tasks. Concerning verbal tasks, there was no significant difference in results across the groups. However, the length of alcohol dependence did significantly predict performance on the RAVLT recognition task indicating possible frontal lobe deficits and disordered recall. Correlational analyses indicate that the utilit

How do cannabis users mentally travel in time? Evidence from an fMRI study of episodic future thinking

Rationale Episodic future thinking (EFT) is a cognitive function that allows individuals to imagine novel experiences that may happen in the future. Prior studies show that EFT is impaired in different groups of substance users. However, there is no evidence regarding the neurobiological mechanisms of EFT in cannabis users. Objectives We aimed to compare brain activations of regular cannabis users and non-using controls during an EFT fMRI task. Exploratory analyses were also conducted to investigate the association between EFT and cannabis use variables (e.g., duration of use, age onset, frequency of use). Methods Twenty current cannabis users and 22 drug-naïve controls underwent an fMRI scanning session while completing a task involving envisioning future-related events and retrieval of past memories as a control condition. The EFT fMRI task was adapted from the autobiographical interview and composed of 20 auditory cue sentences (10 cues for past and 10 cues for future events). Participants were asked to recall a past or generate a future event, in response to the cues, and then rate their vividness after each response. Results We found that cannabis users compared to non-user controls had lower activation within the cerebellum, medial and superior temporal gyrus, lateral occipital cortex, and occipital fusiform gyrus while envisioning future events. Cannabis users rated the vividness of past events significantly lower than non-users (P < 0.005). There were marginal group differences for rating the vividness of future events (P = 0.052). Significant correlations were also found between the medial and superior temporal gyrus activities and behavioral measures of EFT and episodic memory. Conclusions Cannabis users, compared to drug-naïve controls, have lower brain activation in EFT relevant regions. Thus, any attempts to improve aberrant EFT performance in cannabis users may benefit from EFT training