Functional brain imaging in 14 patients with dissociative amnesia reveals right inferolateral prefrontal hypometabolism

Amnesic disorders

Memory disturbances frequently occur after brain damage, but can be associated with psychiatric illnesses as well. Amnesia--the most severe form of memory impairment--has several variants, including anterograde and retrograde amnesia, material-specific and modality-specific amnesia, and transient global amnesia. We searched databases to obtain an overview of amnesia research from the past 5 years. Research into amnesia has increased exponentially, probably because of the availability of modern brain-imaging techniques. In line with the view that memory is not a unity but is organised into several systems, amnesia is described as a multifaceted disease with a frequently poor prognosis.

The dissociative subtype of posttraumatic stress disorder: rationale, clinical and neurobiological evidence, and implications

BACKGROUND

Clinical and neurobiological evidence for a dissociative subtype of posttraumatic stress disorder (PTSD) has recently been documented. A dissociative subtype of PTSD is being considered for inclusion in the forthcoming Diagnostic and Statistical Manual of Mental Disorders-Fifth Edition (DSM-5) to address the symptoms of depersonalization and derealization found among a subset of patients with PTSD. This article reviews research related to the dissociative subtype including antecedent, concurrent, and predictive validators as well as the rationale for recommending the dissociative subtype.

METHODS

The relevant literature pertaining to the dissociative subtype of PTSD was reviewed.

RESULTS

Latent class analyses point toward a specific subtype of PTSD consisting of symptoms of depersonalization and derealization in both veteran and civilian samples of PTSD. Compared to individuals with PTSD, those with the dissociative subtype of PTSD also exhibit a different pattern of neurobiological response to symptom provocation as well as a differential response to current cognitive behavioral treatment designed for PTSD.

CONCLUSIONS

We recommend that consideration be given to adding a dissociative subtype of PTSD in the revision of the DSM. This facilitates more accurate analysis of different phenotypes of PTSD, assist in treatment planning that is informed by considering the degree of patients' dissociativity, will improve treatment outcome, and will lead to much-needed research about the prevalence, symptomatology, neurobiology, and treatment of individuals with the dissociative subtype of PTSD.

The impairment of recollection in functional amnesic states

INTRODUCTION

Functional amnesia refers to various forms of amnesia, which have no direct organic brain basis. Psychological stress and trauma were etiologically linked to its development across various cultures.

METHODS

We have studied several patients with functional amnesia, employing neuropsychological and neuroimaging methods. Herein we provide a review of the current understanding of the phenomenology, neuropsychology and neurobiology of functional amnesia, which we illustrate by reference to five own case descriptions and other cases presented in the literature.

RESULTS

Functional amnesia is mostly of retrograde nature and presents in the form of a memory blockade or repression to recollect episodic-autobiographical events, which may cover the whole past life. Sometimes, the recollection impairment is localized to certain time epochs. In comparison to functional retrograde amnesia, functional isolated anterograde amnesia is much rarer and data on its neurobiology are scant. In patients with functional amnesia with pronounced retrograde episodic-autobiographical memory impairments, we identified changes in brain metabolism, above all reductions in the temporo-frontal regions of the right hemisphere. Recently, even subtle structural changes in the white matter of the (right) frontal cortex were described in functional retrograde amnesia by other researchers.

CONCLUSIONS

The disruption in recollection in functional amnesia is often accompanied by changes in personality dimensions, pertaining to cognition (self-related processing, theory of mind), autonoetic consciousness and affectivity. This suggests that functional amnesia is a multifaceted condition. We hypothesize that the recollection deficit in functional retrograde amnesia primarily reflects a desynchronization between a frontal lobe system, important for autonoetic consciousness, and a temporo-amygdalar system, important for evaluation and emotions. Despite assumptions that functional amnesia can always be reversed, several cases of functional amnesia were found to follow a chronic course, suggesting a need for longitudinal prospective studies to quantify possible global cognitive deterioration over time and its neural underpinnings.

The remains of the day in dissociative amnesia

Memory is not a unity, but is divided along a content axis and a time axis, respectively. Along the content dimension, five long-term memory systems are described, according to their hierarchical ontogenetic and phylogenetic organization. These memory systems are assumed to be accompanied by different levels of consciousness. While encoding is based on a hierarchical arrangement of memory systems from procedural to episodic-autobiographical memory, retrieval allows independence in the sense that no matter how information is encoded, it can be retrieved in any memory system. Thus, we illustrate the relations between various long-term memory systems by reviewing the spectrum of abnormalities in mnemonic processing that may arise in the dissociative amnesia—a condition that is usually characterized by a retrieval blockade of episodic-autobiographical memories and occurs in the context of psychological trauma, without evidence of brain damage on conventional structural imaging. Furthermore, we comment on the functions of implicit memories in guiding and even adaptively molding the behavior of patients with dissociative amnesia and preserving, in the absence of autonoetic consciousness, the so-called “internal coherence of life”.

Psychogenic non-epileptic seizures: a model of their pathogenic mechanism

Psychogenic non-epileptic seizures (PNES) consist of paroxystic events facilitated by a dysfunction in emotion processing. Models explaining the pathogenic mechanisms leading to these seizure-like episodes are limited. In this article, evidence that supports dysfunction at the level of arousal tolerance, cognitive-emotional information processing and volitional control is reviewed. A hypothetical pathophysiological mechanism is discussed based on functional neuroimaging evidence from PNES-related conditions and traits. This pathophysiological model suggests an alteration in the influence and connection of brain areas involved in emotion processing onto other brain areas responsible for sensorimotor and cognitive processes. Integrating this information, PNES are conceptualized as brief episodes facilitated by an unstable cognitive-emotional attention system. During the episodes, sensorimotor and cognitive processes are modified or not properly integrated, allowing the deployment of autonomous prewired behavioral tendencies. Finally, I elaborate on how therapeutic applications could be modified based on the proposed hypothetical model, potentially improving clinical outcomes.

Amygdala in action: relaying biological and social significance to autobiographical memory

The human amygdala is strongly embedded in numerous other structures of the limbic system, but is also a hub for a multitude of other brain regions it is connected with. Its major involvement in various kinds of integrative sensory and emotional functions makes it a cornerstone for self-relevant biological and social appraisals of the environment and consequently also for the processing of autobiographical events. Given its contribution to the integration of emotion, perception and cognition (including memory for past autobiographical events) the amygdala also forges the establishment and maintenance of an integrated self. Damage or disturbances of amygdalar connectivity may therefore lead to disconnection syndromes, in which the synchronous processing of affective and cognitive aspects of memory is impaired. We will provide support for this thesis by reviewing data from patients with a rare experiment of nature - Urbach-Wiethe disease - as well as other conditions associated with amygdala abnormalities. With respect to memory processing, we propose that the amygdala's role is to charge cues so that mnemonic events of a specific emotional significance can be successfully searched within the appropriate neural nets and re-activated.

Losing memories overnight: a unique form of human amnesia

Since an automobile accident in 2005, patient FL has reported difficulty retaining information from one day to the next. During the course of any given day, she describes her memory as normal. However, memory for each day disappears during a night of sleep. She reports good memory for events that occurred before the accident. Although this pattern of memory impairment is, to our knowledge, unique to the medical literature, it was depicted in the fictional film "50 First Dates". On formal testing, FL performed moderately well when trying to remember material that she had learned during the same day, but she exhibited no memory at all for material that she knew had been presented on a previous day. For some tests, unbeknownst to FL, material learned on the previous day was intermixed with material learned on the same day as the test. On these occasions, FL's memory was good. Thus, she was able to remember events from earlier days when memory was tested covertly. FL performed differently in a number of ways from individuals who were instructed to consciously feign her pattern of memory impairment. It was also the impression of those who worked with FL that she believed she had the memory impairment that she described and that she was not intentionally feigning amnesia. On the basis of her neuropsychological findings, together with a normal neurological exam, normal MRI findings, and psychiatric evaluation, we suggest that FL exhibits a unique form of functional amnesia and that its characterization may have been influenced by knowledge of how amnesia was depicted in a popular film. She subsequently improved (and began retaining day-to-day memory) at Johns Hopkins University where she was in a supportive in-patient environment and was shown how to take control of her condition by interrupting her sleep at 4-h intervals.

Searching for the Anatomy of Dissociative Amnesia

Brain damage was traditionally seen as the product of a neurological disease or injury. Nevertheless, modern brain imaging techniques have provided increasing evidence for alterations in brain tissue and metabolism for a number of psychiatric disorders. Though for a while “dissociated” ( Spiegel, 2006 ) from the clinical and scientific arena, dissociative disorders have in the last several years received a renewed interest among several groups of researchers, who embarked on the work of disentangling their neural correlates. We review data from our own research as well as others, which point to distinct changes in brain regions underlying dissociative amnes(t)ic disorders. These changes may consist of overall reductions in brain metabolism or more selective alterations primarily in the right temporo-frontal cortices. Recent evidence with refined magnetic resonance imaging techniques furthermore reveals selective fiber degenerations in these regions. While these changes may persist and probably even intensify in some patients, they may be reversible in others – especially if treatment is carried out successfully within short time after onset. Implications of these findings for the pathogenetic conceptualization of dissociative amnes(t)ic disorders are outlined.