逆行性遗忘、额叶与远期记忆的组织

通过对一例严重记忆障碍合并额叶损伤病人的逆行性遗忘的分析,对远期记忆的组织特点进行了探讨。被试的额叶功能受损较为明显。除顺行性遗忘外,患者的逆行性遗忘也较为严重。对病人进行的逆行性遗忘检测包括：著名人物测验、著名事件、一般知识测验和自传性记忆测验等。被试对著名人物、著名事件的回忆和再认成绩、以及有关个人的情节和语义记忆成绩均较低,但没有典型的随时间下降的趋势,而是呈平直斜率;患者儿童期的自传性记忆和公众事件记忆也受损。这两个特点均与内侧颞叶一间脑系统损伤的特点不同,提示额叶参与了远期记忆的提取等过程。     

Regional cerebral blood flow response to recognition memory versus semantic classification tasks

Two randomly assigned groups, N = 7 each, of neurologically normal patients were composed. One group, RM, had regional cerebral blood flow measurements during a recognition memory probe test; the other group, SC, had rCBF measurements during a semantic classification task, using the same stimulus and response features as the RM task. Thus, the groups differed only in the cognitive instruction they were executing. The RM group showed a significantly lower change from resting baseline to activation, in mean left hemisphere initial slope index, than did the SC group. The RM group, but not the SC group, showed a significant inverse correlation between occipital flow and accuracy of memory performance as indicated by d′. Correlations between age and hemispheric initial slope index, and between homologous left and right hemisphere sites, were also described. The results are considered to support an anatomical basis for the distinction between episodic and semantic memory and to suggest that occipital flow may diminish with accurate memory performance because of an upstream demand of blood in the medial temporal lobes.     

The anatomy of amnesia: neurohistological analysis of three new cases

The most useful information about the anatomy of human memory comes from cases where there has been extensive neuropsychological testing followed by detailed post-mortem neurohistological analysis. To our knowledge, only eight such cases have been reported (four with medial temporal lobe damage and four with diencephalic damage). Here we present neuropsychological and post-mortem neurohistological findings for one patient (NC) with bilateral damage to the medial temporal lobe and two patients (MG, PN) with diencephalic damage due to bilateral thalamic infarction and Korsakoff's syndrome, respectively. All three patients exhibited a similar phenotype of amnesia with markedly impaired declarative memory (anterograde and retrograde) but normal performance on tests of nondeclarative memory (e.g., priming and adaptation-level effects) as well as on tests of other cognitive functions. Patient NC had damage to the hippocampus (dentate gyrus and the CA1 and CA3 fields) and layer III of the entorhinal cortex, but with relative sparing of the CA2 field and the subiculum. Patient MG had damage to the internal medullary lamina and mediodorsal thalamic nuclei. Patient PN had damage to the mammillary nuclei, mammillothalamic tracts, and the anterior thalamic nuclei. These findings illuminate several issues regarding the relation between diencephalic and medial temporal lobe amnesia, the status of recognition memory in amnesia, and the neuroanatomy of memory.     

Perirhinal cortex lesions produce retrograde amnesia for spatial information in rats: consolidation or retrieval?

Several lines of evidence in humans and experimental animals suggest that the hippocampus is critical for the formation and retrieval of spatial memory. However, although the hippocampus is reciprocally connected to adjacent cortices within the medial temporal lobe and they, in turn, are connected to the neocortex, little is known regarding the function of these cortices in memory. Here, using a reference spatial memory task in the radial maze, we show that neurotoxic perirhinal cortex lesions produce a profound retrograde amnesia when learning-surgery intervals of 1 or 50 d are used (Experiment 1). With the aim of dissociating between consolidation and retrieval processes, we injected lidocaine either daily after training (Experiment 2) or before a retention test once the learning had been completed (Experiment 3). Results show that reversible perirhinal inactivation impairs retrieval but not consolidation. However, the same procedure followed in Experiment 2 disrupted consolidation when the lidocaine was injected into the dorsal hippocampus. The results of Experiment 4 rule out the possibility that the deficit in retrieval is due to a state-dependent effect. These findings demonstrate the differential contribution of various regions of the medial temporal lobe to memory, suggesting that the perirhinal cortex plays a key role in the retrieval of spatial information for a long period of time.     

Nonverbal Amnesia and Asymmetric Cerebral Lesions Following Encephalitis

Global amnesia after herpes simplex encephalitis has been typically associated with lesions of anterior and medial temporal lobe, inferior and medial frontal lobe, and insula. The neuropathologic correlates of this disease are usually considered to be bilateral and similar across cases. We describe a 27-year-old woman whose chronic amnesia and cerebral lesions after viral encephalitis indicate a different pattern. Two features distinguish her presentation: (1) markedly asymmetric lesions extensively involving the right temporal lobe but sparing almost all of the same structures on the left and (2) severe compromise of nonverbal learning and a nonverbal retrograde amnesia in contrast to disproportionately small impairments of verbal learning and retention. The findings suggest that encephalitis patients cannot be treated as a homogeneous group and that detailed analysis of variability in their anatomic lesions may be an important explanatory factor in neural accounts of these severe human amnesias.     

Different types of working memory binding in epilepsy patients with unilateral anterior temporal lobectomy

The medial temporal lobe is an important structure for long-term memory formation, but its role in working memory is less clear. Recent studies have shown hippocampal involvement during working memory tasks requiring binding of information. It is yet unclear whether this is limited to tasks containing spatial features. The present study contrasted three binding conditions and one single-item condition in patients with unilateral anterior temporal lobectomy.A group of 43 patients with temporal lobectomy (23 left; 20 right) and 20 matched controls were examined with a working memory task assessing spatial relational binding (object–location), non-spatial relational binding (object–object), conjunctive binding (object–colour) and working memory for single items. We varied the delay period (3 or 6 s), as there is evidence showing that delay length may modulate working memory performance.The results indicate that performance was worse for patients than for controls in both relational binding conditions, whereas patients were unimpaired in conjunctive binding. Single-item memory was found to be marginally impaired, due to a deficit on long-delay trials only.In conclusion, working memory binding deficits are found in patients with unilateral anterior temporal lobectomy. The role of the medial temporal lobe in working memory is not limited to tasks containing spatial features. Rather, it seems to be involved in relational binding, but not in conjunctive binding. The medial temporal lobe gets involved when working memory capacity does not suffice, for example when relations have to be maintained or when the delay period is long.     

Neural correlates of feigned memory impairment are distinguishable from answering randomly and answering incorrectly: an fMRI and behavioral study

Previous functional magnetic resonance imaging (fMRI) studies have identified activation in the prefrontal-parietal-sub-cortical circuit during feigned memory impairment when comparing with truthful telling. Here, we used fMRI to determine whether neural activity can differentiate between answering correctly, answering randomly, answering incorrectly, and feigned memory impairment. In this study, 12 healthy subjects underwent block-design fMRI while they performed digit task of forced-choice format under four conditions: answering correctly, answering randomly, answering incorrectly, and simulated feigned memory impairment. There were three main results. First, six areas, including the left prefrontal cortex, the left superior temporal lobe, the right postcentral gyrus, the right superior parietal cortex, the right superior occipital cortex, and the right putamen, were significantly modulated by condition type. Second, for some areas, including the right superior parietal cortex, the right postcentral gyrus, the right superior occipital cortex, and the right putamen, brain activity was significantly greater in feigned memory impairment than answering randomly. Third, for the areas including the left prefrontal cortex and the right putamen, brain activity was significantly greater in feigned memory impairment than answering incorrectly. In contrast, for the left superior temporal lobe, brain activity was significantly greater in answering incorrectly than feigned memory impairment. The results suggest that neural correlates of feigned memory impairment are distinguishable from answering randomly and answering incorrectly in healthy subjects.     

Remembering versus knowing during face recognition in unilateral temporal lobe epilepsy patients with or without hippocampal sclerosis

Recognition memory involves knowing an item was learned (familiarity) and remembering contextual details about the prior learning episode (recollection). We tested three competing hypotheses about the role of the hippocampus in recollection and familiarity. It mediates either recollection or familiarity, or serves both processes. We further tested whether the left temporal lobe mediates recollection and the right temporal lobe familiarity (modes of processing view), or whether the two temporal lobes mediate remembering material specifically (material specificity view). We investigated 24-h face recognition using the "remember-know" procedure. We studied 23 left and 24 right temporal lobe epilepsy (LTLE/RTLE) patients with and without hippocampal sclerosis (HS+/HS-) and 31 healthy participants. HS+ patients made fewer know responses than HS- patients or healthy participants. RTLE was related to fewer remember responses than LTLE. Our results suggest the hippocampus has a critical role in familiarity. Further, our findings support the material specificity hypothesis of laterality.     

Preserved ability to recognize keywords related to remote events in the absence of retrieval of relevant knowledge: a case of postencephalitic amnesia

We describe a case of severe anterograde and retrograde amnesia resulting from herpes simplex encephalitis. Magnetic resonance imaging revealed pathological changes in the bilateral hippocampi, parahippocampal gyri, fusiform gyri, medial temporal poles, posterior part of the cingulate gyri, and insula. The patient showed severe amnesia for autobiographical episodic memory in relation to events that had occurred throughout her life, but temporally graded amnesia for autobiographical semantic memory, and severe amnesia without a temporal gradient for public events and famous people. However, using a multiple-choice method, she showed a high level of accuracy when choosing keywords related to public or personal events, although this did not prompt her recollection of the events. An important indication of these results is that, even with severe retrograde amnesia, memories of past events are not completely lost. We propose that an event may be stored in a fragmented form, consisting of many components, and that normal recall of an event may require recombination or reconstruction of these components.     

The role of the human medial temporal lobe in object recognition and object discrimination.

This paper reviews evidence from neuropsychological patient studies relevant to two questions concerning the functions of the medial temporal lobe in humans. The first is whether the hippocampus and the adjacent perirhinal cortex make different contributions to memory. Data are discussed from two patients with adult-onset bilateral hippocampal damage who show a sparing of item recognition relative to recall and certain types of associative recognition. It is argued that these data are consistent with Aggleton and Brown's (1999) proposal that familiarity-based recognition memory is not dependent on the hippocampus but is mediated by the perirhinal cortex and dorso-medial thalamic nucleus. The second question is whether the recognition memory deficit observed in medial temporal lobe amnesia can be explained by a deficit in perceptual processing and representation of objects rather than a deficit in memory per se. The finding that amnesics were impaired at recognizing, after short delays, patterns that they could successfully discriminate suggests that their memory impairment did not result from an object-processing deficit. The possibility remains, however, that the human perirhinal cortex plays a role in object processing, as well as in recognition memory, and data are presented that support this possibility.     

The role of the human medial temporal lobe in object recognition and object discrimination

This paper reviews evidence from neuropsychological patient studies relevant to two questions concerning the functions of the medial temporal lobe in humans. The first is whether the hippocampus and the adjacent perirhinal cortex make different contributions to memory. Data are discussed from two patients with adult-onset bilateral hippocampal damage who show a sparing of item recognition relative to recall and certain types of associative recognition. It is argued that these data are consistent with Aggleton and Brown's (1999) proposal that familiarity-based recognition memory is not dependent on the hippocampus but is mediated by the perirhinal cortex and dorso-medial thalamic nucleus. The second question is whether the recognition memory deficit observed in medial temporal lobe amnesia can be explained by a deficit in perceptual processing and representation of objects rather than a deficit in memory per se. The finding that amnesics were impaired at recognizing, after short delays, patterns that they could successfully discriminate suggests that their memory impairment did not result from an object-processing deficit. The possibility remains, however, that the human perirhinal cortex plays a role in object processing, as well as in recognition memory, and data are presented that support this possibility.     

Regional cerebral blood flow response during rest and memory activation in a patient with global amnesia

A college professor with a classical amnesic syndrome is described. He has a WAIS IQ of 130, but dramatic memory loss for episodes ranging from a few seconds ago all the way back to portions of his childhood. The amnesia was of sudden onset, 2 years prior to the current memory tests and regional cerebral blood flow measurements. The etiology is believed, though not conclusively proven, to be medial thalamic infarction. rCBF measurements were taken on six separate occasions, four resting baseline, one memory activation, using the previous procedure of Wood, Taylor, et al., and one carbon dioxide activation. The resting baseline showed extremely low flows throughout the cortex, with some hyperfrontal response on the first baseline. With CO₂ activation, however, there was brisk, uniform reactivity, with all sites showing increased flow. This suggested that there were no prominent areas of impaired vasomotor control or probable ischemic damage in the cortical surface. During memory activation, there was also a generalized increase in flow, especially in the frontal areas. This was in sharp contrast to the pattern for normals, described by Wood, Taylor, et al., which shows a slight overall decrease in flow from baseline to memory activation. The results are interpreted in light of Talland's proposal that the amnesic syndrome reflects an arousal failure, with premature closure and shutdown of memory processing, especially at retrieval. Here the arousal failure is interpreted as an inadequate restriction or focusing of cortical activation, with resulting pathologically diffuse flow increases.     

Episodic memory, amnesia, and the hippocampal-anterior thalamic axis

By utilizing new information from both clinical and experimental (lesion, electrophysiological, and gene-activation) studies with animals, the anatomy underlying anterograde amnesia has been reformulated. The distinction between temporal lobe and diencephalic amnesia is of limited value in that a common feature of anterograde amnesia is damage to part of an "extended hippocampal system" comprising the hippocampus, the fornix, the mamillary bodies, and the anterior thalamic nuclei. This view, which can be traced back to Delay and Brion (1969), differs from other recent models in placing critical importance on the efferents from the hippocampus via the fornix to the diencephalon. These are necessary for the encoding and, hence, the effective subsequent recall of episodic memory. An additional feature of this hippocampal-anterior thalamic axis is the presence of projections back from the diencephalon to the temporal cortex and hippocampus that also support episodic memory. In contrast, this hippocampal system is not required for tests of item recognition that primarily tax familiarity judgements. Familiarity judgements reflect an independent process that depends on a distinct system involving the perirhinal cortex of the temporal lobe and the medial dorsal nucleus of the thalamus. In the large majority of amnesic cases both the hippocampal-anterior thalamic and the perirhinal-medial dorsal thalamic systems are compromised, leading to severe deficits in both recall and recognition.     

内侧颞叶与来源记忆

来源记忆不同于项目记忆。早期的研究认为来源记忆的神经基础主要是前额叶,但近几年的相关研究发现内侧颞叶在来源记忆中的作用也是相当重要的,健康被试的功能神经成像研究和内侧颞叶损伤病人研究都为内侧颞叶在来源记忆中的作用提供了可靠证据。     

Retrograde amnesia in patients with hippocampal, medial temporal, temporal lobe, or frontal pathology

There is considerable controversy concerning the theoretical basis of retrograde amnesia (R.A.). In the present paper, we compare medial temporal, medial plus lateral temporal, and frontal lesion patients on a new autobiographical memory task and measures of the more semantic aspects of memory (famous faces and news events). Only those patients with damage extending beyond the medial temporal cortex into the lateral temporal regions showed severe impairment on free recall remote memory tasks, and this held for both the autobiographical and the more semantic memory tests. However, on t-test analysis, the medial temporal group was impaired in retrieving recent autobiographical memories. Within the medial temporal group, those patients who had combined hippocampal and parahippocampal atrophy (H+) on quantified MRI performed somewhat worse on the semantic tasks than those with atrophy confined to the hippocampi (H-), but scores were very similar on autobiographical episodic recall. Correlational analyses with regional MRI volumes showed that lateral temporal volume was correlated significantly with performance on all three retrograde amnesia tests. The findings are discussed in terms of consolidation, reconsolidation, and multiple trace theory: We suggest that a widely distributed network of regions underlies the retrieval of past memories, and that the extent of lateral temporal damage appears to be critical to the emergence of a severe remote memory impairment.     

Effects of level of retrieval success on recall-related frontal and medial temporal lobe activations

Brain dedicated single photon emission computed tomography (SPECT) was used to compare the neuroactivation produced by the cued recall of response words in a set of studied word pairs with that produced by the cued retrieval of words semantically related to unstudied stimulus words. Six of the 12 subjects scanned were extensively trained so as to have good memory of the studied pairs and the remaining six were minimally trained so as to have poor memory. When comparing episodic with semantic retrieval, the well-trained subjects showed significant left medial temporal lobe activation, which was also significantly greater than that shown by the poorly trained subjects, who failed to show significant medial temporal lobe activation. In contrast, the poorly trained subjects showed significant bilateral frontal lobe activation, which was significantly greater than that shown by the well-trained subjects who failed to show significant frontal lobe activation. The frontal activations occurred mainly in the dorsolateral region, but extended into the ventrolateral and, to a lesser extent, the frontal polar regions. It is argued that whereas the medial temporal lobe activation increased as the proportion of response words successfully recalled increased, the bilateral frontal lobe activation increased in proportion to retrieval effort, which was greater when learning had been less good.     

Short-term and long-term memory deficit following intracarotid Amytal injection: Further support for the memory consolidation hypothesis

To test the three main hypotheses of the human amnesic syndrome (encoding, consolidation, retrieval), we designed an original protocol for memory assessment under Amytal that included, in addition to a retrograde memory measure, both short-term and long-term anterograde memory measures. Twenty epileptic patients with SEEG-confirmed unilateral temporal lobe foci were given right and left injections on successive days. Only the long-term memory measure for material presented under Amytal was significantly related to the presence of a temporal contralateral epileptogenic focus, even if it was assessed when the hemisphere had completely recovered from the effect of Amytal. Short-term memory deficits were observed equally often after injections ipsilateral and contralateral to the epileptogenic focus, and no retrograde amnesia was observed. These results are consistent with the consolidation hypothesis.     

Comparisons between forms of amnesia: some deficits are unique to Korsakoff's syndrome

Certain features of abnormal memory, which have figured prominently in theoretical treatments of the amnesic syndrome, were assessed in patients with Korsakoff's syndrome, in Case N.A., and in patients receiving electroconvulsive therapy. Patients with Korsakoff's syndrome differed from the other patients by (a) failing to exhibit release from proactive interference, and (b) being disproportionately impaired in the ability to make judgments about the temporal order of recent events. These deficits appear to be related to frontal lobe damage and are superimposed on a more basic memory disorder. Theories of amnesia should be founded on the basic memory disorder and not on deficits such as these, which have no obligatory relationship to amnesia. Dissociations between aspects of memory, revealed by the study of amnesia, can also shed light on the organization of memory in the brain.     

A positron emission tomography (PET) study of autobiographical memory retrieval

Memory for the experiences of one's life, autobiographical memory (AM), is one of the most human types of memory, yet comparatively little is known of its neurobiology. A positron emission tomography (PET) study of AM retrieval revealed that the left frontal cortex was significantly active during retrieval (compared to memory control tasks), together with activation in the inferior temporal and occipital lobes in the left hemisphere. We propose that this left frontal lobe activation reflects the operation of control processes that modulate the construction of AMs in posterior neocortical networks.     

The neural basis of autobiographical and semantic memory: new evidence from three PET studies

A novel, neuropsychologically informed paradigm (extended retrieval of events in response to a cue word) was used to investigate the neural basis of autobiographical and semantic memory. Contrasting retrieval of autobiographical memories with retrieval of semantic facts (ABM-SEM) in 24 subjects across three PET studies revealed bilateral involvement of the middle temporal gyrus (BA 21) and medial frontal cortex (BA 9/10). The opposite contrast, SEM-ABM, resulted in increased regional cerebral blood flow in left posterior temporal regions (BA 37) and left prefrontal cortex (BA 45/46). Laterality maps suggest that the bilateral pattern seen in our studies, but not often in other neuroimaging investigations, reflects the use of a task stressing retrieval of specific personal events. Further comparisons revealed that the activation in the right anterior temporal lobe during autobiographical recall was virtually identical to that seen during retrieval of information about famous people or events in contrast with retrieval of general semantic facts. These findings suggest that the retrieval of an autobiographical event requires participation from conceptual knowledge, and that this type of knowledge is bilaterally distributed in the temporal lobes.