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PubMed1991

Double dissociation of short-term and long-term memory for nonverbal material in Parkinson's disease and global amnesia. A further analysis.

The traditional concept of memory disorder is deficiency of the long-term (LTM) but not short-term (STM) component of memory. STM impairment with LTM sparing is seldom reported. The present study investigated STM and LTM for nonverbal material in three neurological conditions associated with memory impairment: bilateral medial temporal lobe lesions (patient H.M.), Parkinson's disease (PD) and Alzheimer's disease (AD). Subjects received 3 tests of nonverbal memory: forward block span, immediate and delayed recall of the Wechsler Memory Scale drawings, and immediate and delayed recognition of abstract designs. Compared with the normal control group, the patient groups displayed different patterns of sparing and loss of the two components of memory: in PD, only STM was impaired; in medial temporal lobe amnesia, only LTM was impaired; and in AD, STM and LTM were both impaired. The contrasting patterns of sparing and loss of STM and LTM in PD and global amnesia were present for both recognition and recall. These results provide evidence that STM and LTM are dissociable processes and are served by separate neurological systems: STM depends upon intact corticostriatal systems, whereas LTM depends upon intact medial temporal lobe systems.

Aged↗
PubMed1992

Focal retrograde amnesia following bilateral temporal lobe pathology. A neuropsychological and magnetic resonance study.

A patient who suffered a severe closed head injury was left with a dense retrograde amnesia for events which she had experienced prior to her injury, but she showed only mild, patchy anterograde memory impairment. Her retrograde amnesia included both public events and autobiographical material, and it extended back to her childhood. Previously learned skills such as playing a piano and driving a car were spared, even though she had no recollection at all of the original learning experience. A series of focused magnetic resonance scan images revealed major pathology in the anterior portion of both temporal lobes. No significant abnormality was found in the hippocampus, thalamus or other medial structures in the limbic-diencephalic system. Our findings indicate the independence of anterograde and retrograde memory mechanisms, and point to structures and pathways in the anterior temporal lobes as playing a critical role in memory for past events.

Adult↗
PubMed1993

Autobiographical amnesia resulting from bilateral paramedian thalamic infarction. A case study in cognitive neurobiology.

A patient with a chronic amnesic state resulting from bilateral paramedian thalamic infarction showed a pattern of retrograde amnesia not previously reported. Personally relevant autobiographical memory was profoundly impaired, whereas knowledge of famous people and public events was relatively spared. Furthermore, knowledge of famous people, including the ability to make accurate temporal judgements, was less affected than knowledge of public events. In addition, we have documented a severe and systematic distortion of personal memory. These findings are not compatible with current accounts of retrograde amnesia based either upon the type of information stored (e.g. episodic versus semantic memory), or upon simple storage versus access models. We propose an explanation based upon an interactive cognitive model in which the patient shows a disorder at the 'thematic retrieval framework' level of memory organization due to a disconnection of frontal and medial temporal memory systems.

Aged↗
PubMed1994

Right frontal cortex hypometabolism in transient global amnesia. A PET study.

A 60-year-old lady with previous hypertension was studied with PET in the acute (early recovery) phase of an otherwise typical episode of transient global amnesia (TGA). Follow-up over > 1 year was uneventful, and delayed CT scans and MRI showed no brain damage. No medical cause was disclosed despite extensive work-up. The PET study revealed a matched reduction in cerebral blood flow and oxygen consumption over the entire lateral frontal cortex on the right side, with an associated, less significant reduction in ipsilateral thalamic and lentiform nucleus metabolism, but sparing the hippocampal area. These changes, which had resolved at a repeat PET study 3 months later, suggest right prefrontal metabolic depression, possibly secondary to thalamic dysfunction, as the underlying mechanism for TGA in this case, consistent with the emerging involvement of the prefrontal cortex in strategies or control of memory traces retrieval. Thus, in analogy with permanent amnesia, TGA may be a core syndrome with several possible foci of dysfunction along the neuronal networks that subserve explicit memory. In the future, combined PET neuropsychological assessment in the acute stage of TGA may prove useful in defining distinct neuropsychological-topographical subtypes of this intriguing clinical entity.

Amnesia↗
PubMed1996

Disorientation in amnesia. A confusion of memory traces.

Disorientation is a common phenomenon in delirium and amnesia. It is thought to have an obvious explanation, i.e. disoriented patients fail to store the information crucial for the maintenance of orientation. In this study, we explored whether disorientation was indeed associated with a failure to learn new information or rather with a confusion of information within memory. Twenty-one patients with severe amnesia were examined. Orientation was tested with a 20-item questionnaire. Two runs of a continuous recognition task were used to test the ability to acquire information (first run of the task) and the tendency to confuse the temporal context of information acquisition (comparison of the second with the first run). We found that orientation was much better predicted by the measure of temporal context confusion (r = 0.90) than by the ability to simply acquire information (r = 0.54). Superimposition of neuroradiological scans demonstrated that increased temporal context confusion was associated with medial orbitofrontal or basal forebrain damage; patients with normal levels of temporal context confusion did not have damage to these areas. We conclude that disorientation more often indicates a confusion of memory traces from different events, i.e. increased temporal context confusion, than an inability to learn new information. Disorientation appears to reflect primarily a failure of the orbitofrontal contribution to memory.

Adult↗
PubMed1997

Severe anterograde amnesia with onset in childhood as a result of anoxic encephalopathy.

Our patient (M.S.) had an abrupt onset of amnesia due to a respiratory arrest at the age of 8 years and has been followed by one of us (A.L.R.) for 19 years. A specially designed MRI study indicated that the neuroanatomical localization of his lesion is restricted to the hippocampal formation bilaterally. Comparison of M.S.'s present IQ and academic scores with earlier scores revealed that his literacy skills, certain basic language functions and vocabulary development were arrested by his memory disorder. In contrast, development of mathematical skill was less curtailed, and verbal and nonverbal logical abilities developed to adult levels. Neuropsychological examination at the age of 27 years elicited a pattern of memory deficits similar to those found in a case (H.M.) of known mesial temporal lobe damage in adulthood. The neuropsychological pattern revealed those aspects of cognitive development that do, and those that do not, require intact memory. The limitations to intellectual development imposed by severe amnesia in childhood are not pervasive, but rather, are limited to specific types of abilities.

Adult↗
PubMed2001

Different patterns of autobiographical memory loss in semantic dementia and medial temporal lobe amnesia: a challenge to consolidation theory.

Temporally graded retrograde memory loss, with a disproportionate impairment of recent relative to remote memories, is considered a hallmark of medial temporal lobe amnesia. According to consolidation theory, the hippocampal complex, which includes the hippocampal formation, parahippocampal gyrus, the entorhinal and perirhinal cortex, plays a time-limited role in memory, needed only until consolidation in the neocortex is complete (Squire, Psychological Review 1992; 99: 195-231). Recent support for this theory comes from findings of a reverse gradient in people with semantic dementia with neocortical degeneration but a relatively preserved hippocampal complex (Hodges and Graham, Neuropsychologia 1998; 36: 803-25). Consolidation theory is challenged by evidence that remote autobiographical memory is not always spared in amnesia (Nadel and Moscovitch, Current Opinion in Neurobiology 1997; 7: 217-27) and that semantic memory becomes highly personalized in semantic dementia (Snowden et al., Memory 1995; 3: 225-46). According to Nadel and Moscovitch, the hippocampal complex is needed to retain and retrieve detailed memories of autobiographical episodes no matter how old they are. To test consolidation theory against the opposing view, we investigated the role of the hippocampal complex in recent and remote autobiographical and personal semantic memory by contrasting the memory of a semantic dementia patient, EL, with that of an amnesic patient, KC, using family photographs as recall cues. KC demonstrated a complete loss of autobiographical episodes with a sparing of autobiographical facts; EL demonstrated well-preserved memory for episodes with a reverse gradient for personally relevant names. The influence of autobiographical significance on memory for names of public figures was examined further by comparing the effect that familiarity and recollection had on recognition of names of famous people and famous places. EL's memory was influenced by autobiographical significance, whereas KC's was not. We propose that the hippocampal complex plays a permanent role in the storage and retrieval of autobiographical episodes and that autobiographical significance may affect semantic representations.

Aged↗
PubMed2001

Severe anterograde amnesia with extensive hippocampal degeneration in a case of rapidly progressive frontotemporal dementia.

Frontotemporal dementia (FTD) is usually characterized as a spectrum of relatively slowly progressive disorders with largely focal frontal or temporal presentations. The development of clinical and research criteria for discriminating FTD from Alzheimer's disease has relied, in part, on the relative preservation of episodic memory in FTD. We present a patient with FTD who, in addition to the more typical behavioural and language deficits, had a profound anterograde amnesia at the time of diagnosis. Neuroimaging confirmed atrophy of frontal and temporal lobes bilaterally, most marked in the anterior left temporal region. At post-mortem, non-Alzheimer pathology resulting in devastating cell loss was revealed in the hippocampi, as well as in the frontal and temporal cortex, thus providing neuroanatomical corroboration of the episodic memory deficit. Progression of the disease was extraordinarily rapid, with just 2 years between reported onset and time of death. This case demonstrates that the pattern of FTD may include severe anterograde amnesia as a prominent and early consequence of the disease.

Amnesia, Anterograde↗
PubMed2000

Measurement properties of the Galveston Orientation and Amnesia Test (GOAT) and improvement patterns during inpatient rehabilitation.

OBJECTIVES: To determine the measurement properties of the Galveston Orientation and Amnesia Test (GOAT) using the Rasch model and rating scale analysis (RSA). DESIGN: Calibration of data collected weekly during rehabilitation. SETTING: Six inpatient rehabilitation facilities. PARTICIPANTS: 77 patients admitted for their first rehabilitation after traumatic brain injury. RESULTS: Rescoring the items as dichotomies, three strata of posttraumatic amnesia (PTA) were identified. All items cohered to define a single construct and the item hierarchy confirmed their hypothesized ordering. CONCLUSIONS: Equal-interval measures of PTA were developed that exhibited good reliability and validity. A self-scoring key was developed to more efficiently assess PTA.

Adolescent↗
PubMed2001

Predicting duration of posttraumatic amnesia (PTA) from early PTA measurements.

OBJECTIVES: To determine a set of variables that would reliably predict duration of posttraumatic amnesia (PTA) in patients with traumatic brain injury and to test the efficacy of the model. DESIGN: Simultaneous standard multiple regression analyses. PARTICIPANTS: Two independent samples of patients with traumatic brain injury who were in the early stages of PTA: a test sample (n = 61) and a cross-validation sample (n = 25). MAIN OUTCOME MEASURE: The Modified Oxford PTA Scale (MOPTAS) is a 12-item test measuring orientation (8 items) and anterograde memory (4 items). The Galveston Orientation and Amnesia Test (GOAT) was also used on a subset of the test sample. PROCEDURE: Patients were examined daily until they emerged from PTA. RESULTS: A statistically significant model, using three predictor variables, was derived that reliably predicted duration of PTA, accounting for 89% of the variance. A second model, using two predictor variables readily available to the clinician (day posttrauma on which PTA testing began and aggregate PTA scores over the first 5 days of testing) had comparable predictive accuracy. A third model, using GOAT data, was also statistically significant and successfully accounted for 72% of the variance. The MOPTAS model showed excellent application to an independent (validation) sample, with an intraclass correlation coefficient between observed and predicted durations of PTA of 0.95. Regression equations for all three models are provided to enable calculation of the predicted duration of PTA. CONCLUSIONS: These models can be readily applied in clinical practice and will provide clinically useful estimates of the duration of PTA within the first week of testing after admission to rehabilitation. This information will be important in terms of family counseling and planning of rehabilitation programs.

Adolescent↗
PubMed1997

Duration of transient amnesia correlates with cognitive outcome in acute encephalitis.

Temporary periods of amnesia are encountered in acute encephalitides. We investigated the association between transient encephalitic amnesia (TENA) and outcome in 60 patients. Twenty-six patients had TENA lasting < or = 1 day (short TENA), 17 had TENA lasting 2-7 days, and 17 had TENA for > 7 days (long TENA). The long TENA group had more neuropsychological impairment, larger brain lesions, and more difficulty in daily activities than the short TENA group. The findings were not explained by the number of epileptic seizures, delay of acyclovir medication, or the aetiology of encephalitis. TENA is a useful new clinical tool in predicting the outcome of acute encephalitis and selecting patients who are in need of detailed neuropsychological evaluation.

Acute Disease↗
PubMed1999

Rhinal cortex, but not medial thalamic, lesions cause retrograde amnesia for objects in rats.

Male Long-Evans rats were trained on five separate object discrimination problems at different times prior to surgery. Following surgery, retrograde amnesia was assessed by measuring retention of the preoperatively learned discrimination problems in lesioned rats and controls. Rats with rhinal cortex lesions displayed temporally graded retrograde amnesia; retention of object discriminations acquired in the recent past (i.e. 2 or 9 days prior to surgery) was significantly impaired, whereas retention of object discriminations acquired more remotely (i.e. 16, 37, or 58 days prior to surgery) was not. In contrast, rats with mediodorsal thalamic lesions exhibited normal savings of all discrimination problems. These results suggest that the rhinal cortex, but not the mediodorsal thalamus, plays a time-limited role in the consolidation of object memory.

Amnesia, Retrograde↗
PubMed2001

Semantic acquisition without memories: evidence from transient global amnesia.

Transient global amnesia (TGA), characterised by a profound anterograde amnesia, is a model of interest to study the acquisition of novel meanings independent of episodic functioning. Three patients were tested during a TGA attack, two in the early recovery phase and the third during the acute phase of TGA, with a semantic priming task involving a restructuring process of conceptual knowledge. During TGA, all patients demonstrated priming effects. Results obtained the day after the episode with the same task showed that these effects persisted at least one day. Episodic memory seems not to be critical for the formation of novel connections among unrelated semantic representations, in accordance with Tulving's model of memory, i.e. episodic memory is not necessary for the acquisition of semantic information.

Acute Disease↗
PubMed1986

Amnesia or fugue state: a diagnostic dilemma.

We report the case of a 16-year-old boy whose presenting symptoms were total retrograde amnesia. After finding no evidence for organic causes, including toxic-metabolic derangements, epilepsy, encephalitis, vasculitis, trauma, or CNS neoplasm, it was determined that the child experienced a psychogenic fugue state with a spontaneous recovery in memory over several days. Although rare, fugue state should be considered in the differential diagnosis of amnesia.

Adolescent↗
PubMed1979

The Galveston Orientation and Amnesia Test. A practical scale to assess cognition after head injury.

The Galveston Orientation and Amnesia Test (GOAT) was developed to evaluate cognition serially during the subacute stage of recovery from closed head injury. This practical scale measures orientation to person, place, and time, and memory for events preceding and following the injury. The distribution of test scores in 50 patients who had recovered from a mild closed head injury was used to define the range of variation in performance and to analyze the effects of demographic factors. In a validity study of 52 closed head-injured patients, the duration of impaired GOAT scores was strongly related to the acute neurosurgical ratings of eye opening, motor responding, and verbal responding on the Glasgow Coma Scale. Duration of post-traumatic amnesia, as defined by the persistence of defective GOAT scores, was longer in patients with computed tomographic evidence of diffuse or bilateral brain injury as compared to cases with focal unilateral lesions. Serial GOAT scores were also predictive of long term level of recovery. Review of the brief cognitive test literature disclosed that several techniques have adequate validity data substantiating their use in the detection of dementia in geriatric, psychiatric, and medical populations. Recommendations for the clinical application of the various brief cognitive tests are discussed.

Adolescent↗
PubMed1998

Transient global amnesia: a complication of incremental exercise testing.

Incremental exercise testing is routinely used for diagnosis, rehabilitation, health screening, and research. We report the case of a 71-yr-old patient with chronic obstructive pulmonary disease (COPD) who suffered an episode of transient global amnesia (TGA) several minutes after successfully completing an incremental exercise test on a cycle ergometer. TGA, which is known to be precipitated by physical or emotional stress in about one-third of cases, is a transient neurological disorder in which memory impairment is the prominent deficit. TGA has a benign course and requires no treatment although 24-h observation is recommended. Recognition of TGA as a potential complication of incremental graded exercise testing is important to both aid diagnosis of the amnesia and to spare a patient unnecessary evaluation.

Aged↗
PubMed2004

Marijuana-induced transient global amnesia.

A 6-year-old boy accidentally became intoxicated with marijuana secondary to ingesting cookies laced with marijuana. He presented with retentive memory deficit of sudden onset that was later diagnosed as transient global amnesia. Transient global amnesia as a result of marijuana intoxication is an extremely rare event.

Acute Disease↗
PubMed1997

Amnesia and neglect: beyond the Delay-Brion system and the Hebb synapse.

Hippocampal damage in people causes impairments of episodic memory, but in rats it causes impairments of spatial learning. Experiments in macaque monkeys show that these two kinds of impairment are functionally similar to each other. After any lesion that interrupts the Delay-Brion system (hippocampus, fornix, mamillary bodies and anterior thalamus) monkeys are impaired in scene-specific memory, where an event takes place against a background that is specific to that event. Scene-specific memory in the monkey corresponds to human episodic memory, which is the memory of a unique event set in a particular scene, as opposed to scene-independent human knowledge, which is abstracted from many different scenes. However, interruption of the Delay-Brion system is not sufficient to explain all of the memory impairments that are seen in amnesic patients. To explain amnesia the specialized function of the hippocampus in scene memory needs to be considered alongside the other, qualitatively different functional specializations of other memory systems of the temporal lobe, including the perirhinal cortex and the amygdala. In all these specialized areas, however, including the hippocampus, there is no fundamental distinction between memory systems and perceptual systems. In explaining memory disorders in amnesia it is also important to consider them alongside the memory disorders of neglect patients. Neglect patients fail to represent in memory the side of the world that is contralateral to the current fixation point, in both short- and long-term memory retrieval. Neglect was produced experimentally by unilateral visual disconnection in the monkey, confirming the idea that visual memory retrieval is retinotopically organized; patients with unilateral medial temporal-lobe removals showed lateralized memory impairments for half-scenes in the visual hemifield contralateral to the removal. Thus, in scene-memory retrieval the Delay-Brion system contributes to the retrieval of visual memories into the retinotopically organized visual cortex. This scene memory interpretation of hippocampal function needs to be contrasted with the cognitive-map hypothesis. The cognitive-map model of hippocampal function shares some common assumptions with the Hebb-synapse model of association formation, and the Hebb-synapse model can be rejected on the basis of recent evidence that monkeys can form direct associations in memory between temporally discontiguous events. Our general conclusion is that the primate brain encompasses widespread and powerful memory mechanisms which will continue to be poorly understood if theory and experimentation continue to concentrate too much, as they have in the past, on the hippocampus and the Hebb synapse.

Amnesia↗