Temporal Lobe Damage Research Articles

A Rapid, Hippocampus-Dependent, Item-Memory Signal that Initiates Context Memory in Humans

SummaryThe hippocampus, a structure located in the temporal lobes of the brain, is critical for the ability to recollect contextual details of past episodes. It is still debated whether the hippocampus also enables recognition memory for previously encountered context-free items. Brain imaging [1, 2] and neuropsychological patient studies [3, 4] have both individually provided conflicting answers to this question. We overcame the individual limitations of imaging and behavioral patient studies by combining them and observed a novel relationship between item memory and the hippocampus. We show that interindividual variability of hippocampal volumes in a large patient population with graded levels of hippocampal volume loss and controls correlates with context, but not item-memory performance. Nevertheless, concurrent measures of brain activity using magnetoencephalography reveal an early (350 ms) but sustained hippocampus-dependent signal that evolves from an item signal into a context memory signal. This is temporally distinct from an item-memory signal that is not hippocampus dependent. Thus, we provide evidence for a hippocampus-dependent item-memory process that initiates context retrieval without making a substantial contribution to item recognition performance. Our results reconcile contradictory evidence concerning hippocampal involvement in item memory and show that hippocampus-dependent mnemonic processes are more rapid than previously believed.

It does not look odd to me: Perceptual impairments and eye movements in amnesic patients with medial temporal lobe damage

Studies of people with memory impairments have shown that a specific set of brain structures in the medial temporal lobe (MTL) is vital for memory function. However, whether these structures have a role outside of memory remains contentious. Recent studies of amnesic patients with damage to two structures within the MTL, the hippocampus and the perirhinal cortex, indicated that these patients also performed poorly on perceptual tasks. More specifically, they performed worse than controls when discriminating between objects, faces and scenes with overlapping features. In order to investigate whether these perceptual deficits are reflected in their viewing strategies, we tested a group of amnesic patients with MTL damage that included the hippocampus and perirhinal cortex on a series of oddity discrimination tasks in which they had to select an odd item from a visual array. Participants' eye movements were monitored throughout the experiment. Results revealed that patients were impaired on tasks that required them to discriminate between items that shared many features, and tasks that required processing items from different viewpoints. An analysis of their eye movements revealed that they exhibited a similar viewing pattern as controls: they fixated more on the target item on trials answered correctly, but not on trials answered incorrectly. In addition, their impaired performance was not explained by an abnormal viewing-strategy that assessed their use of working memory. These results suggest that the perceptual deficits in the MTL patients are not a consequence of abnormal viewing patterns of the objects and scenes, but instead, could involve an inability to bind information gathered from several fixations into a cohesive percept. These data also support the view that MTL structures are important not only for long-term memory, but are also involved in perceptual tasks.

Default Network Connectivity in Medial Temporal Lobe Amnesia

There is substantial overlap between the brain regions supporting episodic memory and the default network. However, in humans, the impact of bilateral medial temporal lobe (MTL) damage on a large-scale neural network such as the default mode network is unknown. To examine this issue, resting fMRI was performed with amnesic patients and control participants. Seed-based functional connectivity analyses revealed robust default network connectivity in amnesia in cortical default network regions such as medial prefrontal cortex, posterior medial cortex, and lateral parietal cortex, as well as evidence of connectivity to residual MTL tissue. Relative to control participants, decreased posterior cingulate cortex connectivity to MTL and increased connectivity to cortical default network regions including lateral parietal and medial prefrontal cortex were observed in amnesic patients. In contrast, somatomotor network connectivity was intact in amnesic patients, indicating that bilateral MTL lesions may selectively impact the default network. Changes in default network connectivity in amnesia were largely restricted to the MTL subsystem, providing preliminary support from MTL amnesic patients that the default network can be fractionated into functionally and structurally distinct components. To our knowledge, this is the first examination of the default network in amnesia.

Anevrizma Nedeniyle Opere Edilen Hastada Gelişen Organik Kişilik Sendromu: Bir Olgu Sunumu / Organıc Personalıty Dısorder After The Aneurysm Surgery: A Case Report

Complex and persistant neuropsychiatric symptoms may appear due to different causes affecting certain parts of the brain. They may sometimes present as a psychiatric disorder without neurological symptoms. Organic personality disorder is one of the psychiatric disorder following traumatic brain injury. Affective instability, impulsivity, agression, apathy or paranoid thoughts are basic symptoms. In this paper, we report a case with psychiatric symptoms developed 2 months after the middle cerebral artery aneurysm surgery and considered due to the possible damage of the right medial temporal lobe.

FMRI of verbal and nonverbal memory processes in healthy and epileptogenic medial temporal lobes

Material‐specific memory impairments are a well-established consequence of unilateral medial temporal lobe damage. We used fMRI to investigate encoding and recognition of verbal and nonverbal stimuli using adaptations of tasks used successfully in clinical evaluations of patients with temporal lobe epilepsy (TLE). We studied two patient groups, one with left TLE and one with right TLE, and one group of healthy subjects. Results from the healthy subjects indicated that initial and delayed recognition trials of the verbal task activated the left medial temporal lobe, and the same tasks of the nonverbal task activated the right, confirming the sensitivity to laterality of our clinical tasks. Patients tended to use the opposite hippocampus, but often the parahippocampal gyrus on the same side, compared to the healthy subjects. Since our patients and the healthy groups performed similarly on the memory tasks, we conclude that the patients' activation patterns represent an effective adaptation to the presence of an unhealthy hippocampus.

On remembering and forgetting our autobiographical pasts: Retrograde amnesia and Andrew Mayes’s contribution to neuropsychological method

Andrew Mayes’s contribution to the neuropsychology of memory has consisted in steadily teasing out the nature of the memory deficit in the amnesic syndrome. This has been done with careful attention to matters of method at all stages. This particularly applies to his investigations of forgetting rates in amnesia and to his studies of retrograde amnesia. Following a brief outline of his work, the main current theories of retrograde amnesia are considered: consolidation theory, episodic-to-semantic shift theory, and multiple trace theory. Findings across the main studies in Alzheimer dementia are reviewed to illustrate what appears to be consistently found, and what is much more inconsistent. A number of problems and issues in current theories are then highlighted—including the nature of the temporal gradient, correlations with the extent of temporal lobe damage, what we would expect ‘normal’ remote memory curves to look like, how they would appear in focal retrograde amnesia, and whether we can pinpoint retrograde amnesia to hippocampal/medial temporal damage on the basis of existing studies. A recent study of retrograde amnesia is re-analysed to demonstrate temporal gradients on recollected episodic memories in hippocampal/medial temporal patients. It is concluded that there are two requirements for better understanding of the nature of retrograde amnesia: (i) a tighter, Mayesian attention to method in terms of both the neuropsychology and neuroimaging in investigations of retrograde amnesia; and (ii) acknowledging that there may be multiple factors underlying a temporal gradient, and that episodic and semantic memory show important interdependencies at both encoding and retrieval. Such factors may be critical to understanding what is remembered and what is forgotten from our autobiographical pasts.

Can complex visual discrimination deficits in amnesia be attributed to the medial temporal lobe? An investigation into the effects of medial temporal lobe damage on brain connectivity

It has been suggested that complex visual discrimination deficits in patients with medial temporal lobe (MTL) damage may be explained by damage or dysfunction beyond the MTL. We examined the resting functional networks and white matter connectivity of two amnesic patients who have consistently demonstrated discrimination impairments for complex object and/or spatial stimuli across a number of studies. Although exploratory analyses revealed some significant differences in comparison with neurologically healthy controls (more specifically in the patient with a larger MTL lesion), there were no obvious findings involving posterior occipital or posterior temporal regions, which can account entirely for their discrimination deficits. These findings converge with previous work to support the suggestion that the MTL does not subserve long-term declarative memory exclusively. © 2012 Wiley Periodicals, Inc.

Intact Memory for Irrelevant Information Impairs Perception in Amnesia

SummaryMemory and perception have long been considered separate cognitive processes, and amnesia resulting from medial temporal lobe (MTL) damage is thought to reflect damage to a dedicated memory system. Recent work has questioned these views, suggesting that amnesia can result from impoverished perceptual representations in the MTL, causing an increased susceptibility to interference. Using a perceptual matching task for which fMRI implicated a specific MTL structure, the perirhinal cortex, we show that amnesics with MTL damage including the perirhinal cortex, but not those with damage limited to the hippocampus, were vulnerable to object-based perceptual interference. Importantly, when we controlled such interference, their performance recovered to normal levels. These findings challenge prevailing conceptions of amnesia, suggesting that effects of damage to specific MTL regions are better understood not in terms of damage to a dedicated declarative memory system, but in terms of impoverished representations of the stimuli those regions maintain.

Visual Working Memory Capacity and the Medial Temporal Lobe

Patients with medial temporal lobe (MTL) damage are sometimes impaired at remembering visual information across delays as short as a few seconds. Such impairments could reflect either impaired visual working memory capacity or impaired long-term memory (because attention has been diverted or because working memory capacity has been exceeded). Using a standard change-detection task, we asked whether visual working memory capacity is intact or impaired after MTL damage. Five patients with hippocampal lesions and one patient with large MTL lesions saw an array of 1, 2, 3, 4, or 6 colored squares, followed after 3, 4, or 8 s by a second array where one of the colored squares was cued. The task was to decide whether the cued square had the same color as the corresponding square in the first array or a different color. At the 1 s delay typically used to assess working memory capacity, patients performed as well as controls at all array sizes. At the longer delays, patients performed as well as controls at small array sizes, thought to be within the capacity limit, and worse than controls at large array sizes, thought to exceed the capacity limit. The findings suggest that visual working memory capacity in humans is intact after damage to the MTL structures and that damage to these structures impairs performance only when visual working memory is insufficient to support performance.

Better Together

Better Together

Comprehension of concrete and abstract words in patients with selective anterior temporal lobe resection and in patients with selective amygdalo-hippocampectomy

The role of the anterior temporal lobe (ATL) in semantic memory is now firmly established. There is still controversy, however, regarding the specific role of this region in processing various types of concepts. There have been reports of patients suffering from semantic dementia (SD), a neurodegenerative condition in which the ATL is damaged bilaterally, who present with greater semantic impairment for concrete concepts than for abstract concepts, an effect known as reversal of the concreteness effect. This effect has previously been interpreted as reflecting degraded visual–perceptual features of objects due to damage to the inferior temporal lobes such as is observed in SD. Temporal lobe atrophy in SD, however, is bilateral even if it usually predominates to the left ATL, and it has been found to extend beyond the ATL, throughout the temporal lobes including medial and posterior temporal lobe regions. The question therefore remains whether greater impairment for concrete concepts results from damage to the ATL or from damage to the visual association cortex, and if unilateral damage can produce such a deficit.The aim of the present study was to investigate the processing of concrete and abstract words in rare patients who underwent a selective ATL surgical resection, and to compare their performance with that of patients with selective medial temporal lobe damage sparing the ATL region. Seven patients with a selective unilateral anterior temporal resection (ATL), 15 patients with a selective unilateral amygdalo-hippocampectomy (SeAH), and 15 healthy age- and education-matched controls underwent detailed neuropsychological assessment and carried out a semantic similarity judgment task evaluating their comprehension of concrete and abstract words. Results showed that both ATL and SeAH groups were significantly impaired on the semantic task relative to the control group. Within the patient groups, however, comprehension of concrete words was significantly more impaired than that of abstract words in the ATL group, while comprehension of abstract and concrete words was equally affected in the SeAH group. Results of this study suggest that the ATL region may play a critical role in processing concrete concepts, and that the reversal of the concreteness effect observed in ATL patients may result from damage to a categorical organization underlying the representation of concrete concepts.

Semantic memory is impaired in patients with unilateral anterior temporal lobe resection for temporal lobe epilepsy.

Contemporary clinical and basic neuroscience studies have increasingly implicated the anterior temporal lobe regions, bilaterally, in the formation of coherent concepts. Mounting convergent evidence for the importance of the anterior temporal lobe in semantic memory is found in patients with bilateral anterior temporal lobe damage (e.g. semantic dementia), functional neuroimaging and repetitive transcranial magnetic stimulation studies. If this proposal is correct, then one might expect patients with anterior temporal lobe resection for long-standing temporal lobe epilepsy to be semantically impaired. Such patients, however, do not present clinically with striking comprehension deficits but with amnesia and variable anomia, leading some to conclude that semantic memory is intact in resection for temporal lobe epilepsy and thus casting doubt over the conclusions drawn from semantic dementia and linked basic neuroscience studies. Whilst there is a considerable neuropsychological literature on temporal lobe epilepsy, few studies have probed semantic memory directly, with mixed results, and none have undertaken the same type of systematic investigation of semantic processing that has been conducted with other patient groups. In this study, therefore, we investigated the semantic performance of 20 patients with resection for chronic temporal lobe epilepsy with a full battery of semantic assessments, including more sensitive measures of semantic processing. The results provide a bridge between the current clinical observations about resection for temporal lobe epilepsy and the expectations from semantic dementia and other neuroscience findings. Specifically, we found that on simple semantic tasks, the patients' accuracy fell in the normal range, with the exception that some patients with left resection for temporal lobe epilepsy had measurable anomia. Once the semantic assessments were made more challenging, by probing specific-level concepts, lower frequency/more abstract items or measuring reaction times on semantic tasks versus those on difficulty-matched non-semantic assessments, evidence of a semantic impairment was found in all individuals. We conclude by describing a unified, computationally inspired framework for capturing the variable degrees of semantic impairment found across different patient groups (semantic dementia, temporal lobe epilepsy, glioma and stroke) as well as semantic processing in neurologically intact participants.

Working memory, long-term memory, and medial temporal lobe function.

Early studies of memory-impaired patients with medial temporal lobe (MTL) damage led to the view that the hippocampus and related MTL structures are involved in the formation of long-term memory and that immediate memory and working memory are independent of these structures. This traditional idea has recently been revisited. Impaired performance in patients with MTL lesions on tasks with short retention intervals, or no retention interval, and neuroimaging findings with similar tasks have been interpreted to mean that the MTL is sometimes needed for working memory and possibly even for visual perception itself. We present a reappraisal of this interpretation. Our main conclusion is that, if the material to be learned exceeds working memory capacity, if the material is difficult to rehearse, or if attention is diverted, performance depends on long-term memory even when the retention interval is brief. This fundamental notion is better captured by the terms subspan memory and supraspan memory than by the terms short-term memory and long-term memory. We propose methods for determining when performance on short-delay tasks must depend on long-term (supraspan) memory and suggest that MTL lesions impair performance only when immediate memory and working memory are insufficient to support performance. In neuroimaging studies, MTL activity during encoding is influenced by the memory load and correlates positively with long-term retention of the material that was presented. The most parsimonious and consistent interpretation of all the data is that subspan memoranda are supported by immediate memory and working memory and are independent of the MTL.

Perception and Conception: Temporal Lobe Activity during Complex Discriminations of Familiar and Novel Faces and Objects

Recent studies indicate that medial-temporal lobe (MTL) damage, either from focal lesions or neurodegenerative disease (e.g., semantic dementia), impairs perception as well as long-term declarative memory. Notably, however, these two patient groups show different performance for meaningful versus unfamiliar stimuli. In amnesics with nonprogressive MTL lesions, the use of meaningful stimuli, compared with unfamiliar items, boosted discrimination performance. In semantic dementia, a condition characterized by progressive deterioration of conceptual knowledge in the context of anterolateral temporal lobe damage, performance for meaningful stimuli was equivalent to that for unfamiliar items. To further investigate these findings, we scanned healthy volunteers while they performed odd-one-out discriminations involving familiar (i.e., meaningful/famous) and unfamiliar (i.e., novel) objects and faces and a baseline task of size oddity. Outside the scanner, volunteers' recognition memory was assessed. We found above baseline activity in the perirhinal cortex and hippocampus for all object and face discriminations and above baseline activity in the temporal pole for all face discriminations. The comparison of meaningful, relative to novel, faces and objects, revealed increased activity in the perirhinal cortex and hippocampus. In the temporal pole, we also found activity related to meaningfulness for faces but not for objects. Importantly, these meaningfulness effects were evident even for discriminations that were not subsequently well remembered, suggesting that the difference between meaningful and novel stimuli reflects perceptual or conceptual processes rather than solely incidental encoding into long-term memory. The results provide further evidence that the MTL is recruited during complex perceptual discrimination and additionally suggest that these structures are recruited in semantic processing of objects and faces.

Learned control over attention capture is disrupted following medial temporal lobe damage

Learned control over attention capture is disrupted following medial temporal lobe damage

Perceptual and anatomic patterns of selective deficits in facial identity and expression processing

Whether a single perceptual process or separate and possibly independent processes support facial identity and expression recognition is unclear. We used a morphed-face discrimination test to examine sensitivity to facial expression and identity information in patients with occipital or temporal lobe damage, and structural and functional MRI to correlate behavioral deficits with damage to the core regions of the face-processing network. We found selective impairments of identity perception in two patients with right inferotemporal lesions and two prosopagnosic patients with damage limited to the anterior temporal lobes. Of these four patients one exhibited damage to the right fusiform and occipital face areas, while the remaining three showed sparing of these regions. Thus impaired identity perception can occur with damage not only to the fusiform and occipital face areas, but also to other medial occipitotemporal structures that likely form part of a face recognition network. Impaired expression perception was seen in the fifth patient with damage affecting the face-related portion of the posterior superior temporal sulcus. This subject also had difficulty in discriminating identity when irrelevant variations in expression needed to be discounted. These neuropsychological and neuroimaging data provide evidence to complement models which address the separation of expression and identity perception within the face-processing network.

Modulation of encoding and retrieval by recollection and familiarity: Mapping the medial temporal lobe networks

Medial temporal lobe (MTL) structures are crucial for episodic memory. However, it remains unclear how these structures are involved in encoding and retrieval processes as a function of recollection and familiarity. To better elucidate MTL organization of these two processes, we implemented an fMRI protocol in which both encoding and retrieval of words were scanned in 21 healthy adults. During encoding, subjects were requested to bind each word to an emotional context (pleasant or unpleasant). Retrieval consisted of a Remember/Know procedure in two stages: first, subjects had to recognize the word, followed by the retrieval of the associated emotional context. fMRI data were reported in eight manually delineated MTL regions of interest (in the head, body and tail of the hippocampus, the entorhinal, perirhinal and parahippocampal cortices, the amygdala and the temporopolar cortex). Results obtained in 19 subjects showed four MTL patterns of activity consisting in activations of parahippocampal cortex and hippocampus in episodic encoding and retrieval and perirhinal cortex involvement in familiarity. These results are in line with the Binding of Item and Context (BIC) model predictions. Additionally, some new findings specified the familiarity MTL neural substrate by showing precise entorhinal activations during retrieval of familiar words, as well as hippocampal and amygdala deactivations in encoding of these words. Finally, we emphasize that among all four memory processes, episodic retrieval (recollection effect) was the only one eliciting strong bilateral activations in all MTL structures. These results should be considered for future studies on MTL dysfunction in patients with temporal lobe damage.

Multidimensional scaling of emotional responses to music in patients with temporal lobe resection

The present study investigated emotional responses to music by using multidimensional scaling (MDS) analysis in patients with right or left medial temporal lobe (MTL) lesions and matched normal controls (NC). Participants were required to evaluate emotional dissimilarities of nine musical excerpts that were selected to express graduated changes along the valence and arousal dimensions. For this purpose, they rated dissimilarity between pairs of stimuli on an eight-point scale and the resulting matrices were submitted to an MDS analysis. The results showed that patients did not differ from NC participants in evaluating emotional feelings induced by the musical excerpts, suggesting that all participants were able to distinguish refined emotions. We concluded that the ability to detect and use emotional valence and arousal when making dissimilarity judgments was not strongly impaired by a right or left MTL lesion. This finding has important clinical implications and is discussed in light of current neuropsychological studies on emotion. It suggests that emotional responses to music can be at least partially preserved at a non-verbal level in patients with unilateral temporal lobe damage including the amygdala.

Intact Performance on Feature-Ambiguous Discriminations in Rats with Lesions of the Perirhinal Cortex

We developed a behavioral paradigm for the rat that made it possible to separate the evaluation of memory functions from the evaluation of perceptual functions. Animals were given extensive training on an automated two-choice discrimination task and then maintained their memory performance at a high level while interpolated probe trials tested visual perceptual ability. The probe trials systematically varied the degree of feature ambiguity between the stimuli, such that perceptual functions could be tested across 14 different levels of difficulty. As feature ambiguity increased, performance declined in an orderly, monotonic manner (from 87% correct to chance, 50% correct). Bilateral lesions of the perirhinal cortex fully spared the capacity to make feature-ambiguous discriminations and the performance of lesioned and intact animals was indistinguishable at every difficulty level. In contrast, the perirhinal lesions did impair recognition memory. The findings suggest that the perirhinal cortex is important for memory and not for perceptual functions.

Memory, Visual Discrimination Performance, and the Human Hippocampus

We evaluated recent proposals that the hippocampus supports certain kinds of visual discrimination performance, for example, when spatial processing is required and the stimuli have a high degree of feature overlap. Patients with circumscribed hippocampal lesions tried to discriminate between images of similar faces or images of similar scenes. In one condition, elements of the stimulus display repeated from trial to trial, and in another condition every trial was unique. In the repeated condition for both faces and scenes, controls gradually improved their performance across testing. In the trial-unique condition, no improvement occurred. The patients were impaired for both faces and scenes in the repeated condition where controls could benefit from learning. However, the patients were fully intact in the trial-unique condition. The results suggest that previous reports of impaired discrimination performance after medial temporal lobe damage may reflect impaired learning rather than impaired visual perception. The findings support the fundamental idea that memory is a distinct cerebral function separable from other perceptual and cognitive abilities.