Content-specific source encoding in the human medial temporal lobe.

Although the medial temporal lobe (MTL) is known to be essential for episodic encoding, the contributions of individual MTL subregions remain unclear. Data from recognition memory studies have provided evidence that the hippocampus supports relational encoding important for later episodic recollection, whereas the perirhinal cortex has been linked with encoding that supports later item familiarity. However, extant data also strongly implicate the perirhinal cortex in object processing and encoding, suggesting that perirhinal processes may contribute to later episodic recollection of object source details. To investigate this possibility, encoding activation in MTL subregions was analyzed on the basis of subsequent memory outcome while participants processed novel scenes paired with 1 of 6 repeating objects. Specifically, encoding activation correlating with later successful scene recognition memory was evaluated against that of source recollection for the object paired with the scene during encoding. In contrast to studies reporting a link between perirhinal cortex and item familiarity, it was found that encoding activation in the right perirhinal cortex correlates with successful recollection of the paired object. Furthermore, other MTL subregions also exhibited content-specific source encoding patterns of activation, suggesting that MTL subsequent memory effects are sensitive to stimulus category. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Images of medial temporal lobe functions in human learning and memory

Investigations of the neural basis of mammalian memory have focused more often on the medial temporal lobe (MTL) than on any other brain region. In humans, the amnesic syndrome revealed the essential importance of the multiple structures located in the MTL system for declarative memory (the remembrance of events and facts). Other neural systems mediate procedural forms of memory, including delay eyeblink conditioning, which depends on the cerebellum, and cognitive skill learning, which depends on the striatum. We review three functional imaging studies that reveal different patterns of MTL activation associated with declarative and procedural memory tasks. One study shows separate MTL activations during the encoding or retrieval of declarative memories. A second study shows MTL activation that occurs in parallel with cerebellum-dependent delay eyeblink conditioning, but does not appear to influence that form of procedural memory. A third study reveals suppression of the MTL during striatum-dependent cognitive skill learning. These studies provide images of MTL activations that are correlated with, independent from, or antagonistic to memory performance.     

Strategy of evaluation and surgical results in medial temporal lobe epilepsy]

To analyse the presurgical evaluation process of mediotemporal lobe epilepsy (MTLE) in relation to electroclinical characteristics of the patients, we reviewed the presurgical data (clinical, EEG, neuropsychological, MRI, FDG-PET and sometimes intracranial EEG) and the post-operative results of 53 consecutive cases treated by antero-medial temporal resection for MTLE (without lesion other than mediotemporal sclerosis). Forty one patients (77 p. 100) had a typical and well-lateralised presentation and were operated without invasive procedure. Twelve patients (23 p. 100) presented less pure data: unusual or absent auras, divergent scalp EEG features (bitemporal, widespread or extratemporal) or absence of MRI-based hippocampal sclerosis or FDG-PET hypometabolism. They were explored by invasive monitoring which confirmed the medial temporal origin of seizures. Outcome (follow-up: 30 months) was excellent in 88 p. 100 of the pure cases (Engel's class I) and less favorable in the more difficult ones (50 p. 100 of class I). In conclusion, the diagnosis and surgical treatment of MTLE can be performed without invasive investigations in the majority of cases owing to the strong contribution of brain imaging and video EEG monitoring. Some patients however present a less pure presentation suggesting more complex epileptogenic networks and associated to relatively less favorable postsurgical results.     

Human medial temporal lobe in aging: anatomical basis of memory preservation

Nucleotide sequence analyses of polymerase chain reaction-amplified genes were performed to determine whether adaptation of herpes simplex virus type 2 to replication in cultured cells or in internal organs during neonatal disseminated disease results in selection of variants with altered forms of three glycoproteins (gB, gC, or gD) that influence virus entry into cells. No variations in sequence were noted as a consequence of in vitro passage or replication in different organs. Five viruses from different subjects differed with respect to gB, gC, and gD gene sequences, expressing four distinct forms of gB, three of gC, and two of gD. These differences did not confer resistance to neutralization by guinea pig or human antisera from subjects immunized with recombinant gB or gD vaccines and may not be consequential for vaccine development.     

Separate neural bases of two fundamental memory processes in the human medial temporal lobe

The participation of medial temporal-lobe structures in memory performance was examined by functional magnetic resonance imaging of local blood oxygenation level-dependent signals. Signals were measured during encoding into memory complex scenes or line drawings and during retrieval from memory of previously studied line drawings or words. Encoding tasks yielded increased signals for unfamiliar information in a posterior medial-temporal region that were focused in the parahippocampal cortex. Retrieval tasks yielded increased signals for successfully remembered information in an anterior medial-temporal region that were focused in the subiculum. These results indicate that separate components of the human medial temporal-lobe memory system are active during distinct memory processes.     

Intra-individual differences between technetium-99m-HMPAO and technetium-99m-ECD in the normal medial temporal lobe

Regional distributions of 99mTc-hexamethyl propyleneamine oxime (99mTc-HMPAO) and 99mTc-ethyl cysteinate dimer (99mTc-ECD) were compared in the normal brain. METHODS: Six paid, healthy volunteers (mean age 26 yr) had high-resolution neuroperfusion SPECT using both 99mTc-HMPAO and 99mTc-ECD on separate days. RESULTS: Regional distribution of the two tracers differed. Technetium-99m-HMPAO accumulated more in the thalamus, frontal lobe, temporal lobe and cerebellum than 99mTc-ECD, which accumulated more in the occipital and parietal lobes. There was a considerable difference in the accumulation of the two tracers in the medial temporal lobe. The percent accumulations of 99mTc-HMPAO and 99mTc-ECD in the medial temporal lobe compared with the mean global cerebral cortical accumulation were 93.9% +/- 2.4% and 83.1% +/- 4.1% (mean +/- s.d.), respectively. CONCLUSION: The results suggest that 99mTc-HMPAO and 99mTc-ECD require specific and separate criteria for diagnosing temporal lobe pathologies, such as dementia and temporal lobe epilepsy.     

Side of seizure focus predicts left medial temporal lobe activation during verbal encoding

OBJECTIVE: Functional MRI (FMRI) was used to investigate the effect of medial temporal lobe (MTL) pathology on activation of language encoding areas in patients with temporal lobe epilepsy (TLE). METHODS: Whole-brain FMRI was obtained. Twenty-eight patients with either left TLE (LTLE) or right TLE (RTLE) performed a semantic decision task alternating with an auditory perceptual task. RESULTS: Activation of language areas in the frontal and parietal lobes was similar in both groups, with no group differences in the total number of active voxels. However, the RTLE group showed much stronger activation of the left MTL, including the hippocampus, parahippocampal gyrus, and collateral sulcus, than did the LTLE group. CONCLUSIONS: Activation of the left MTL during semantic encoding discriminates patients with RTLE and LTLE. This FMRI technique may potentially be of use in determining memory lateralization and for predicting the side of seizure focus in TLE.     

Visual association encoding activates the medial temporal lobe: a functional magnetic resonance imaging study

The involvement of structures in the medial temporal lobe during the encoding of visual associations was studied with functional magnetic resonance imaging. In 11 out of 12 normal healthy volunteers this task resulted in activation in posterior portions of the parahippocampal region, close to the collateral sulcus. In seven subjects activation was encountered in the hippocampal formation. The visual association task as adapted for this study may provide a sensitive measure to study anterograde amnesia prevalent in Alzheimer's disease. Therefore, the present paradigm enables the study of individual changes in learning and memory capacities over time.     

Relationship between anatomic lesions of the temporal lobe and temporal lobe epilepsy

A structural lesion of the brain is a frequent finding in intractable partial epileptic patients. We analyse anatomo-electro-clinical characteristics of 58 patients in which MR showed a lesion inside the temporal lobe. They are 29 males and 29 females with a mean age at surgery of 23.5 +/- 10.7 years (2.6-45.9). The mean epilepsy duration is of 13.4 +/- 8 years (1.3-35.5), with a mean seizure frequency of 28.7 +/- 43.6 per month, with a great inter-individual variability (from 3 per month to 15 a day). The minimum follow-up is 3.5 years. A video-EEG monitoring was performed in 21 cases, while a stereo-EEG investigation was judged mandatory in 26. On the basis of anatomo-electro-clinical correlations and of the results of presurgical investigations, the epileptogenic area was proved to be temporal in 49 cases, temporal but controlateral to the lesion in 1, and at least bilobar in 8 patients.     

Procedural memory system supports single cue trace eyeblink conditioning in medial temporal lobe amnesia.

A number of studies investigating trace eyeblink conditioning have found impaired, but not eliminated, acquisition of conditioned responses (CRs) in both animals and humans with hippocampal removal or damage. The underlying mechanism of this residual learning is unclear. The present study investigated whether the impaired level of learning is the product of residual hippocampal function or whether it is mediated by another memory system that has been shown to function normally in delay eyeblink conditioning. Performance of bilateral medial temporal lobe amnesic patients who had a prior history of participating in eyeblink conditioning studies was compared to a control group with a similar training history and to an untrained control group in a series of single cue trace conditioning tasks with 500 ms, 250 ms, and 0 ms trace intervals. Overall, patients acquired CRs to a level similar to the untrained controls, but were significantly impaired compared to the trained controls. The pattern of acquisition suggests that amnesic patients may be relying on the expression of previously acquired, likely cerebellar based, procedural memory representations in trace conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early amyloid deposition in the medial temporal lobe of young Down syndrome patients: a regional quantitative analysis

The presence of the neuropathological alterations of Alzheimer's disease (AD) in essentially all older Down syndrome (DS) patients suggests that the examination of younger DS patients may clarify the early pathological progression of AD. We examined the hippocampus and parahippocampal-inferior temporal gyri of 42 DS patients (ages 4 days to 38 years) for the deposition of amyloid beta protein (Abeta) using both a modified Bielschowsky stain and immunohistochemistry for Abeta protein. The parahippocampal and inferior temporal gyri demonstrated Abeta staining in cases as young as 8 years of age. As age and degree of Abeta deposition increased, staining included the CA-1/subiculum and dentate molecular layer followed then by the remainder of the CA hippocampal regions. The first neuritic plaques were observed in the CA-1/subiculum, despite this being a later region of Abeta deposition. Although Abeta staining increased with age, there was substantial variability in the severity of Abeta deposition within age groups. These results suggest that within the hippocampal/parahippocampal region there is a progressive stereotypic deposition of Abeta. The variable severity of Abeta deposition within age groups suggests that other factors, besides DS, may be contributing to the timing and severity of Abeta deposition.     

Memory and imagery in the temporal lobe

Experimental and clinical studies in primates indicate that visual information is stored and retrieved by interactions between the temporal association area and the medial temporal lobe structures. Recent findings from single-neuron recordings have provided new evidence that perceptual aspects of the temporal neocortex are closely related to its memory function based on association. They further suggest that imagery is also implemented by the same neural mechanism that subserves memory retrieval.     

Surgical anatomy of the temporal lobe

The complex functional and anatomic relationships between the structures in and around the temporal lobe are central to the problem of intractable partial complex seizures. Resecting those areas that are responsible for seizures and protecting those that are essential for the normal functioning of the patient are the fundamental tasks of the epilepsy surgeon. A thorough understanding of the structural and functional anatomy of this region is essential to achieve these goals.     

Outcome after temporal lobectomy in bilateral temporal lobe epilepsy

We determined how noninvasive presurgical data relate to prognosis after temporal lobectomy in patients with independent bilateral temporal lobe (IBTL) complex partial seizures on the intracranial electroencephalogram (EEG). Between 1986 and 1994, 28 patients had IBTL seizures on intracranial EEG. Fifteen of these 28 patients underwent temporal lobectomy and 13 were not offered surgery. Of the 15 patients who had surgery, 10 patients became seizure-free. Magnetic resonance imaging (MRI) and the Wada test were the only variables associated with a seizure-free outcome. Seven of 10 seizure-free patients had a lateralized Wada result or the presence of unilateral hippocampal sclerosis, whereas none of the patients with persistent seizures had either of these findings. Variables not found to be predictive of a seizure-free outcome included location of scalp interictal spikes, degree of seizure-onset laterality, presence of early epilepsy risk factor, duration of epilepsy, and full-scale intelligence quotient. We conclude that MRI and the Wada test provide information of prognostic value in patients with bilateral temporal seizures independent of intracranial EEG data.     

Stimulus specific adaptation in inferior temporal and medial temporal cortex of the monkey

We studied the early immunity induced by a live glycoprotein E (gE) negative bovine herpesvirus 1 (BHV1) marker vaccine. Three groups of specific-pathogen-free calves were either not vaccinated, or vaccinated two days or two hours before the introduction of a calf that was intranasally infected with wild-type BHV1 the day before. We quantified the shedding of gE-negative vaccine virus and of wild-type virus, using a double-staining immunoassay. In calves vaccinated two hours before the introduction of the infected calf, the shedding of wild-type virus was reduced, compared with that of the unvaccinated control calves. The shedding of wild-type virus was most significantly reduced in the calves that were vaccinated two days before: only very small amounts of wild-type virus were isolated. Wild-type virus was not detected at all in the samples from one of the five calves of that group. Furthermore, this calf was the only one in which we did not detect antibodies against gE. Hence, intranasal vaccination with a live gE-negative vaccine induced early immunity against a BHV1 contact infection. This suggests that this vaccine can be used efficaciously in the early stages of a BHV1 outbreak.     

Periventricular nodular heterotopia and intractable temporal lobe epilepsy: poor outcome after temporal lobe resection

We describe 5 women and 5 men with periventricular nodular heterotopia and electroclinical features suggestive of temporal lobe epilepsy, who were surgically treated for control of medically refractory seizures. Magnetic resonance imaging revealed bilateral periventricular nodular heterotopia in 7 of the 10 patients. Because of the lack of clear localization, 6 patients were studied with intracranial depth electrode recordings. Seizures were of hippocampal onset (3 patients), regional temporal lobe onset (2 patients), or occipital-temporal onset (1 patient). Anterior temporal lobectomy was performed in 6 patients; selective amygdalohippocampectomy, in 1; and anterior temporal lobectomy plus resection of the heterotopic tissue, in 3. None of the 9 patients followed for more than 12 months postoperatively were seizure free. Two patients were initially seizure free for approximately 18 months, but then seizures recurred. One patient had a major reduction in seizure frequency at a 39-month follow-up after most of the unilateral heterotopic tissue was included in the temporal resection. Temporal resection did not lead to a long-term favorable outcome in this group of patients with periventricular nodular heterotopia and epileptogenic discharges involving the temporal lobe. This suggests a more widespread disorder with epileptogenic activity possibly originating in or near the heterotopic tissue. The clinical and electrographic features of periventricular nodular heterotopia pointing to temporal lobe origin are misleading and temporal resection does not result in long-term cessation of seizures.     

Dynamics of the paroxysmal syndrome in temporal lobe epilepsy

Results of studying the time course of the paroxysmal syndrome based on long-term follow-up of 151 patients with temporal epilepsy are presented. Some regularities of the syndrome course are determined, a rather high degree of the variability of its manifestations over the period of the disease is established, a relative constancy of the aura, transformations of which were noted only in half of the observations, is shown. It is noted that the paroxysmal syndrome is the most developed within a period of 5 to 15 years after the disease onset. Results of conservative therapy are evaluated.     

Stereotaxic surgery of temporal lobe epilepsy

Forty patients with temporal epilepsy were operated on with a stereotaxic technique. Eleven patients had a unilateral localization of the epileptic focus, and in 29 bitemporal foci were diagnosed. In evaluating the results of the treatment the dynamics of the epileptic fits, the peculiarities of changes in the mental status, and the degree of social adaptation were taken into consideration. A postoperative improvement was achieved in 73% of the patients with monotemporal lesions, while in those with bitemporal epilepsy and distinct persistent mental disorders the state was improved in 44% of the cases. Indications for the choice of the zone of destruction depending on the clinical peculiarities of the lesion are presented.