Visuo-spatial memory tests in right temporal lobe epilepsy foci: clinical validity.

OBJECTIVE: To examine the appropriateness of visual memory tests as an identification method for right mesial temporal lobe dysfunctions in an epilepsy patient group and to study the relationship and possible overlap with non-memory cognitive domains and demographic variables. METHODS: Eighty preoperative candidates with mesial temporal lobe epilepsy (TLE) were examined using the "Corsi Block-Tapping Test", "Diagnosticum für Cerebralschädigung" (DCS), the path subtest of the "Verbaler und Visueller Merkfähigkeitstest" (VVM), and the Rey-Osterrieth Complex Figure Test (ROCF). Factorial analyses were performed on raw scores to determine the effect of epilepsy-related variables, interictal epileptiform discharges (IEDs) and presence of cortical dysgenesis, on visual and verbal memory parameters. Sensitivity, specificity and Receiver Operating Characteristic (ROC) curves were calculated based on normative data. Furthermore, Spearman correlations between memory and non-memory cognitive tasks were performed. RESULTS: The scores for test sensitivity and specificity and the ROC curves illustrate the tests' poor capacity to lateralize the functional deficit zone even when epilepsy-related factors, such as cortical dysgenesis or presence of contralateral IEDs were controlled. Significant correlations were found between the visual memory measures and nonverbal reasoning, processing speed, attentional flexibility, and visual planning. CONCLUSION: These neuropsychological tests are not sensitive enough to lateralize the epileptogenic focus in temporal lobe epilepsy patients since in addition to learning and consolidation processes, they measure additional cognitive domains. These results have implications for clinical neuropsychologists, in terms of test choice and the interpretation in the context of presurgical diagnostics.

Visuoperceptual and visuospatial abilities prior to and after anterior temporal lobectomy: a case study.

We describe a patient who presented with temporal lobe epilepsy and a seizure onset pattern in the right temporo-occipital area. Structural MRI revealed sclerosis in the right hippocampus. A comprehensive presurgical neuropsychological assessment allowed us to disentangle deficits in visual object recognition and visual imagery from well-preserved spatial capacities. Following a right temporal lobectomy, the patient remained seizure free, and 1 year postsurgery, the patient's scores on object recognition and imagery were in the normal range. Our findings suggest that visual object recognition and visual imagery are sustained by cortical areas located in proximity to the temporo-occipital ventral pathway and that perceptual and imagery spatial processing is subserved as well by anatomically close mechanisms. Furthermore, the results seem to indicate that nonlesional paroxysmal activity in the posterior temporal lobe can cause chronic dysfunctions of the visual system and that it may be reversible with effective seizure control.

Do some neurological conditions induce brain plasticity processes?

Paillard [Paillard J. Réflexions sur l'usage du concept de plasticité en Neurobiologie. J Psychol Norm Pathol 1976;1:33-47] defined adaptive plasticity as the capacity of the system to change its own structure and expand its behavioural repertoire. We review the literature on brain damage patients, in whom, adaptive plasticity was observed via neuropsychological and functional neuroimaging examinations. Attentional and memory system alterations and some resulting changes considered as compensatory mechanisms are commented. We have selected a single case presenting with developmental amnesia [Vargha-Khadem F, Gadian DG, Watkins KE, Connelly A, Van Paesschen W, Mishkin M. Differential effects of early hippocampal pathology on episodic and semantic memory. Science 1997;277(5324):376-80; Maguire EA, Vargha-Khadem F, Mishkin M. The effects of bilateral hippocampal damage on fMRI regional activations and interactions during memory retrieval. Brain 2001;124(Pt 6):1156-70] and several groups of multiple sclerosis patients studied recently [e.g. Mainero C, Pantano P, Caramia F, Pozzilli C. Brain reorganization during attention and memory tasks in multiple sclerosis: insights from functional MRI studies. J Neurol Sci 2006;245(1/2):93-8; Morgen K, Sammer G, Courtney SM, Wolters T, Melchior H, Blecker CR, et al. Distinct mechanisms of altered brain activation in patients with multiple sclerosis. Neuroimage 2007;37(3):937-46; Nebel K, Wiese H, Seyfarth J, Gizewski ER, Stude P, Diener HC, et al. Activity of attention related structures in multiple sclerosis patients. Brain Res 2007;1151:150-60]. Convergence evidence via the two approaches - neuropsychological and functional fMRI - was shown as functional and structural brain plasticity was demonstrated in the selected works. Some common characteristics of brain plasticity emerge from this review independently of the neurological conditions we reviewed.

Psychogenic memory deficits associated with functional cerebral changes: an FMRI study.

We studied a case of psychogenic amnesia by means of a functional magnetic resonance imaging (fMRI) experiment involving the retrieval of autobiographical memories. The 38-year-old patient was unable to access most of her autobiographical memories from her childhood up to 16 years of age. Compared with the forgotten period, evocation of the normally retrieved memories elicited increased activity in medial temporal and dorso-lateral frontal regions. Evocation of the preserved scattered recollections was associated with bilaterally distributed temporo-parieto-occipital loci of activations. These functional changes seem to support the idea of common mechanisms involved in both organic and psychogenic amnesias.

Neural correlates of remembering/knowing famous people: an event-related fMRI study.

It has been suggested that knowledge about some famous people depends on both a generic semantic component and an autobiographical component [Westmacott, R., & Moscovitch, M. (2003). The contribution of autobiographical significance to semantic memory. Memory and Cognition, 31, 761-774]. The neuropsychological studies of semantic dementia (SD) and Alzheimer disease (AD) demonstrated that the two aspects are very likely to be mediated by different brain structures, with the episodic component being highly dependent upon the integrity of the medial temporal lobe (MTL) [Westmacott, R., Black, S. E., Freedman, M., & Moscovitch, M. (2004). The contribution of autobiographical significance to semantic memory: Evidence from Alzheimer's disease, semantic dementia, and amnesia. Neuropsychologia, 42, 25-48]. Using an fMRI design in healthy participants, we aimed: (i) to investigate the pattern of brain activations sustaining the autobiographical and the semantic aspects of knowledge about famous persons. Moreover, (ii) we examined if the stimulus material (face/name) influences the lateralisation of the cerebral networks. Our findings suggested that different patterns of activation corresponded to the presence or absence of personal significance linked to semantic knowledge; MTL was engaged only in the former case. Although choice of stimulus material did not influence the hemispheric lateralisation in "classical" terms, it did play a role in engaging different cerebral regions.

Implicit emotion during recollection of past events: a nonverbal fMRI study.

Faces of other significant people are highly self-relevant and close to our everyday way of recollecting past events. We chose such stimuli to probe the emotional component of autobiographical memory retrieval. Photographs were collected from family members without the participant's involvement, thereby avoiding refreshment of the memory trace prior to the scanning session. We asked the subjects to spontaneously evoke a unique autobiographical episode following the presentation of relatives' and friends' faces. Famous faces recognition was used as a semantic memory control task. We carried out a post-fMRI debriefing session to collect participants' memories and their emotional intensity. The post-scanning behavioural data together with the neuroimaging data provided evidence that emotional aspects were implicitly involved during recollections. Our findings suggest that the use of highly self-relevant stimuli and the collection of data with no previous refreshment of the memory trace influence the right lateralisation of activations in the medial temporal lobe (MTL).

Material-independent cerebral network of re-experiencing personal events: evidence from two parallel fMRI experiments.

Two parallel fMRI experiments were conducted with the aim to clarify the lateralisation issue of the cerebral network underlying autobiographical memory retrieval independently of the stimulus material and the refreshment of the memory trace. The verbal experiment required a pre-scanning interview, while the nonverbal version tested the subjects directly during the fMRI session. Both experiments were constructed using the same experimental design to eliminate methodological variables in order to render comparisons possible. We found a predominantly left-lateralised cerebral network independently of material and regardless of whether or not memory traces were reactivated prior to the scanning session. We discuss the results in the context of neuroimaging studies of autobiographical memory (AbM).

Selective memory impairment for public events in a patient with left temporal lobe epilepsy.

Highly selective memory impairment for public events was demonstrated in a patient (JR), who suffered from temporal lobe epilepsy (TLE). We successfully trained JR's memory for a set of news events and discuss, on those bases, the characteristics of news events processing that may have contributed to its increased vulnerability relative to autobiographical memory (AbM).

Focal retrograde amnesia documented with matching anterograde and retrograde procedures.

Focal retrograde amnesia is an unusual and theoretically challenging form of memory disorder. The case of a 65-year-old woman presenting with focal retrograde amnesia is reported. Following a cardiac arrest and subsequent hypoxia she remained in a coma for 24 h with evidence of epileptiform activity during the early recovery period. MR scans, 4 and 7 months post-onset, showed mild bifrontal atrophic changes mainly affecting white matter areas. An [18F]fluorodeoxyglucose resting PET scan 1-year post-onset demonstrated right occipito-temporo-parietal hypometabolism. We were able to document the patient's performance on an extensive range of anterograde and retrograde tests and to monitor her recovery of function by assessing her performance at 4, 12 and 24 months post-onset. Spared anterograde memory was observed on a range of verbal and non-verbal tests, including matched tasks that compared pre-illness and post-illness onset recollections. In contrast, her performance on retrograde memory tests, using detailed autobiographical and public events verbal and photographic tasks, showed a temporally-graded retrograde amnesia, more particularly affecting memory for autobiographical episodes. Possible mechanisms underlying CH's focal retrograde amnesia are discussed in terms of Damasio's time-locked multiregional retroactivation model.

Pure retrograde amnesia following a mild head trauma: a neuropsychological and metabolic study.

After a minor closed head injury, a 33-year-old man acquired extensive retrograde amnesia (RA) covering the previous ten years and concerning autobiographical, semantic and procedural memories. The patient's learning abilities remained excellent and he recovered considerable information from his wife, the media and personal documents. This relearned information did not, however, provide a sense of personal experience in the first weeks. CT and MRI failed to show brain damage, but EEG and SPECT examination showed a marked right temporal dysfunction. After three months the patient had almost completely recovered from RA. Interestingly, a parallel recovery was observed in the second SPECT obtained at this period. There was clearly a blockade of retrieval, while the stored engrams were probably intact. The mechanisms underlying such a functional amnesia are discussed in the light of previous reports of amnesia without brain lesions.

From Augustine of Hippo's Memory Systems to Our Modern Taxonomy in Cognitive Psychology and Neuroscience of Memory: A 16-Century Nap of Intuition before Light of Evidence.

Over the last half century, neuropsychologists, cognitive psychologists and cognitive neuroscientists interested in human memory have accumulated evidence showing that there is not one general memory function but a variety of memory systems deserving distinct (but for an organism, complementary) functional entities. The first attempts to organize memory systems within a taxonomic construct are often traced back to the French philosopher Maine de Biran (1766-1824), who, in his book first published in 1803, distinguished mechanical memory, sensitive memory and representative memory, without, however, providing any experimental evidence in support of his view. It turns out, however, that what might be regarded as the first elaborated taxonomic proposal is 14 centuries older and is due to Augustine of Hippo (354-430), also named St Augustine, who, in Book 10 of his Confessions, by means of an introspective process that did not aim at organizing memory systems, nevertheless distinguished and commented on sensible memory, intellectual memory, memory of memories, memory of feelings and passion, and memory of forgetting. These memories were envisaged as different and complementary instances. In the current study, after a short biographical synopsis of St Augustine, we provide an outline of the philosopher's contribution, both in terms of questions and answers, and focus on how this contribution almost perfectly fits with several viewpoints of modern psychology and neuroscience of memory about human memory functions, including the notion that episodic autobiographical memory stores events of our personal history in their what, where and when dimensions, and from there enables our mental time travel. It is not at all meant that St Augustine's elaboration was the basis for the modern taxonomy, but just that the similarity is striking, and that the architecture of our current viewpoints about memory systems might have preexisted as an outstanding intuition in the philosopher's mind.

MRI-based volumetry correlates of autobiographical memory in Alzheimer's disease.

The aim of the present volumetric study was to explore the neuro-anatomical correlates of autobiographical memory loss in Alzheimer's patients and healthy elderly, in terms of the delay of retention, with a particular interest in the medial temporal lobe structures. Fifteen patients in early stages of the disease and 11 matched control subjects were included in the study. To assess autobiographical memory and the effect of the retention delay, a modified version of the Crovitz test was used according to five periods of life. Autobiographical memory deficits were correlated to local atrophy via structural MRI using Voxel Based Morphometry. We used a 'lateralized index' to compare the relative contribution of hippocampal sub-regions (anterior vs posterior, left vs right) according to the different periods of life. Our results confirm the involvement of the hippocampus proper in autobiographical memory retrieval for both recent and very remote encoding periods, with larger aspect for the very remote period on the left side. Contrary to the prominent left-sided involvement for the young adulthood period, the implication of the right hippocampus prevails for the more recent periods and decreases with the remoteness of the memories, which might be associated with the visuo-spatial processing of the memories. Finally, we suggest the existence of a rostrocaudal gradient depending on the retention duration, with left anterior aspects specifically related to retrieval deficits of remote memories from the young adulthood period, whereas posterior aspects would result of simultaneous encoding and/or consolidation and retrieval deficit of more recent memories.

Experiencing past and future personal events: functional neuroimaging evidence on the neural bases of mental time travel.

Functional MRI was used in healthy subjects to investigate the existence of common neural structures supporting re-experiencing the past and pre-experiencing the future. Past and future events evocation appears to involve highly similar patterns of brain activation including, in particular, the medial prefrontal cortex, posterior regions and the medial temporal lobes. This result seems to support the view of a common neurocognitive system, which would allow humans to mentally travel through time. Past events recollection was associated with greater amplitude of hippocampal and anterior medial prefrontal hemodynamic responses. This result is discussed in terms of the involvement of the self in the conscious experience of past and future events representations. More generally, our data provide new evidence in favour of the idea that re- and pre-experiencing past and future events may rely on similar cognitive capacities.

The neural bases of the constructive nature of autobiographical memories studied with a self-paced fMRI design.

In Conway and Pleydell-Pearce's model (2000), autobiographical memories are viewed as transitory mental representations, more often generated in an effortful way. An important claim of the model concerns the dynamic process that evolves over time, from the left prefrontal areas to posterior regions, to retrieve specific memories. The present work aims at investigating, using fMRI, the temporal distribution of effortful autobiographical memory construction. In addition, a self-paced design was implemented to elucidate the question of the timing window required to evoke recollections. The results showed a large pattern of brain regions, which included the two major poles of activation predicted by Conway and Pleydell-Pearce's model. Likewise, we were able to detect the earlier implication of the left dorso-lateral prefrontal cortex, by comparison with posterior structures, which seemed to confirm its involvement in the effortful retrieval process. Finally, the self-paced procedure allowed us to refine the timing window necessary to construct past events.

One-year postoperative autobiographical memory following unilateral temporal lobectomy for control of intractable epilepsy.

PURPOSE: To examine the effects of temporal lobectomy (TL), particularly concerning its lateralization. METHODS: Patients completed autobiographical memory tests, preoperatively and 1-year postoperatively. RESULTS: (a) right TL (RTL) patients recalled significantly more memories from the year after surgery than from the year before TL; (b) their pre to postoperative improvement on autobiographical memory scores was positively correlated to improvement of delayed story recall scores; and (c) 1 year after surgery, performance on recent personal memory recall was normalized for RTL patients only. CONCLUSION: We suggest that, in the absence of recurrent seizures, the relative integrity of the left hemisphere together with residual right hemisphere structures sustains postoperative autobiographical memory consolidation, at least 1 year postoperatively.

Topographical recognition memory sensitive to amnestic mild cognitive impairment but not to depression.

OBJECTIVE: Amnestic mild cognitive impairment (aMCI) involves episodic memory. The person who presents aMCI has a high risk of developing Alzheimer's disease (AD). However, prediction of deterioration to dementia in cases of aMCI can be confounded with depression due to lack of specificity on selective memory tests. Finding a test sensitive to aMCI but not to depression would be potentially most useful to subsequent longitudinal studies researching the neuropsychological markers of preclinical AD. We hypothesized that the performance on a topographical memory task would be sensitive to the aMCI condition, while depression would not influence such a performance. PARTICIPANTS AND METHODS: A group of 137 community-dwelling French-speaking subjects between 55 and 70 years old was administered a topographical recognition memory task. Based on aMCI and depression criteria, 45 subjects were selected and divided into four groups: 11 patients with aMCI without depression, nine depressive patients with aMCI, ten depressive patients without cognitive impairment and 15 control subjects. The remaining non-selected participants did not belong to any of the previous interest groups. RESULTS: The 'aMCI' factor had a significant effect on the topographical recognition memory task scores, while the 'depression' factor did not. The aMCI patients performed worse than the non-aMCI. CONCLUSION: Although these results were found with relatively small groups, deficits in topographical recognition memory were observed in aMCI patients and did not seem to be sensitive to depression. Further longitudinal studies are needed to examine whether deficits in topographical recognition memory are a neuropsychological marker of preclinical AD.

Remote memory in temporal lobe epilepsy.

PURPOSE: The present study aims at characterizing remote memory in patients with temporal lobe epilepsy (TLE); it also considers the impact of its most important variables (lateralization of the lesion, duration of epilepsy, age at onset, and seizure frequency) on remote memory. METHODS: We examined the performance of 38 patients with unilateral TLE (19 right TLE and 19 left TLE) and 35 healthy subjects on six remote memory tasks. Memory for personal events was assessed by using the Autobiographical Memory Interview and the Modified Crovitz Test. Memory for public events was evaluated by means of photographs of famous faces and famous scenes, questions about famous events, and the Dead/Alive Test. RESULTS: Both right-TLE and left-TLE groups had impaired memory for autobiographic episodes and public events relative to normal subjects. In contrast, personal semantic memory was preserved. In addition, an effect of laterality was recorded, with right-TLE patients obtaining significantly better scores than left-TLE patients on every test. Duration of epilepsy, age at onset, and seizure frequency did not influence performance on remote memory measures. CONCLUSIONS: The comprehensive neuropsychological study of 38 TLE patients showed that this neurologic condition affects remote memory systems differently. We discuss the different factors that could account for this pattern of performance on the bases of both functional brain organization and memory theories.