Lateralized impairment of the emotional enhancement of verbal memory in patients with amygdala-hippocampus lesion

Story reading with incidental comprehension and memory: left hemisphere dominance

BACKGROUND

There are no studies on adults with unilateral brain lesions regarding story reading with incidental/implicit comprehension and memory, in which memory is only assessed through delayed recall. There is a need for validation of cerebral laterality in this type of verbal recall, which includes spontaneous performance (free or uncued condition (UC)), and induced-through-question performance regarding the forgotten units (cued condition (CC)).

OBJECTIVES

To explore the effects of unilateral brain lesions, of oral reading with expression (RE) and comprehension (RC) on delayed recall of a story, as either UC or CC; and to validate the ability of UC and CC to discriminate the side of brain injury.

METHODS

Data were obtained from 200 right-handed volunteers, among whom 42 had left-hemisphere injury (LHI), 49 had right-hemisphere injury (RHI) and 109 were demographically-matched healthy participants (HP). Patients who were unable to read, understand or speak were excluded.

RESULTS

LHI individuals presented impairment of both UC and CC, in relation to the other two groups (non-LHI) with sensitivity and specificity above 70%. LHI and RHI individuals were not significantly different in RE and RC, but they were both different from HP in all the assessments except CC, in which RHI individuals resembled HP. Despite this lack of abnormality in RHI individuals during CC, about half of this group showed impairment in UC. Additionally, whereas RE had a significant effect on UC, the moral of the story (RC) had a significant effect on both UC and CC.

CONCLUSIONS

The left hemisphere was dominant for this memory task involving implicit processing.

The Impact of Right Temporal Lobe Epilepsy On Nonverbal Memory: Meta-regression of Stimulus- and Task-related Moderators

Nonverbal memory tests have great potential value for detecting the impact of lateralized pathology and predicting the risk of memory loss following right temporal lobe resection (TLR) for temporal lobe epilepsy (TLE) patients, but this potential has not been realized. Previous reviews suggest that stimulus type moderates the capacity of nonverbal memory tests to detect right-lateralized pathology (i.e., faces > designs), but the roles of other task-related factors have not been systematically explored. We address these limitations using mixed model meta-regression (k = 158) of right-lateralization effects (right worse than left TLE) testing the moderating effects of: 1) stimulus type (designs, faces, spatial), 2) learning format (single trial, repeated trials), 3) testing delay (immediate or long delay), and 4) testing format (recall, recognition) for three patient scenarios: 1) presurgical, 2) postsurgical, and 3) postsurgical change. Stimulus type significantly moderated the size of the right-lateralization effect (faces > designs) for postsurgical patients, test format moderated the size of the right-lateralization effect for presurgical-postsurgical change (recognition > recall) but learning format and test delay had no right-lateralization effect for either sample. For presurgical patients, none of the task-related factors significantly increased right-lateralization effects. This comprehensive review reveals the value of recognition testing in gauging the risk of nonverbal memory decline.

Verbal emotional memory laterality effect on amygdalohippocampectomy for refractory epilepsy

OBJECTIVES

To study the brain lateralization of the verbal emotional memory and the influence of the emotional valence, we investigated a sample composed of patients with medial temporal lobe refractory epilepsy (MTLE) treated with unilateral amygdalohippocampectomy compared to a control group.

MATERIALS & METHODS

A new task (Verbal Association) was designed and implemented to assess emotional memory performance. It was applied to 62 patients with MTLE of whom 31 have been subjected to right amygdalohippocampectomy and 31 to left amygdalohippocampectomy. These patients were compared with 31 participants with no cerebral pathology, as a control group.

RESULTS

(a) The control group obtained a higher number of recalled words than the rest of the groups, while the MTLE-right group obtained better results than the MTLE-left group. (b) In the case of positive emotional valence words, the MTLE-left group performed significantly worse than the rest of the groups; whereas for negative emotional words, the MTLE-left group presented the lowest average performance and the control group obtained a higher number of recalled words compared to MTLE-right group. In the case of neutral emotional words, no significant differences were found among the groups. (c) The MTLE-left group showed poorer performance on positive and negative words than neutral; the control group demonstrated lower average performance on positive and neutral words compared to negative; the MTLE-right group did not show any significant differences on the recall of different emotional valences.

CONCLUSIONS

Patients with MTLE show a deficit in the verbal recall which is exacerbated for information with an affective component. This deficit is more prominent in the case of patients with left unilateral resection (MTLE-left group) since they lose the benefits of the emotional information for the recall.

Verbal emotional memory in a case with left amygdala damage

The amygdala nuclei appear to be critically implicated in emotional memory. However, in most studies, encoding and consolidation processes cannot be analyzed separately. We thus studied the verbal emotional memory in a young woman with a ganglioglioma of the left amygdala and analyzed its impact (1) on each step of the memory process (encoding, retrieval, and recognition) (2) on short- and long-term consolidation (1-hour and 1-week delay) and (3) on processing of valence (positive and negative items compared to neutral words). Results showed emotional encoding impairments and, after encoding was controlled for, emotional long-term consolidation. Finally, although the negative words were not acknowledged as emotionally arousing by the patient, these words were specifically poorly encoded, recalled, and consolidated. Our data suggest that separate cerebral networks support the processing of emotional versus neutral stimuli.

Memory for emotional material in temporal lobe epilepsy

Several studies suggest that highly emotional information could facilitate long-term memory encoding and consolidation processes via an amygdala-hippocampal network. Our aim was to assess emotional perception and episodic memory for emotionally arousing material in patients with temporal lobe epilepsy (TLE) who are candidates for surgical treatment. We did this by using an audiovisual paradigm. Forty-six patients with medically resistant TLE (26 with left TLE and 20 with right TLE) and 19 healthy controls were assessed with a standard narrative test of emotional memory. The experimental task consisted of sequential picture slides with an accompanying narrative depicting a story that has an emotional central section. Subjects were asked to rate their emotional arousal reaction to each stimulus after the story was shown, while emotional memory (EM) was assessed a week later with a multiple choice questionnaire and a visual recognition task. Our results showed that ratings for emotional stimuli for the patients with TLE were significantly higher than for neutral stimuli (p=0.000). It was also observed that patients with TLE recalled significantly less information from each slide compared with controls, with a trend to lower scores on the questionnaire task for the group with LTLE, as well as poorer performance on the visual recognition task for the group with RLTE. Emotional memory was preserved in patients with RTLE despite having generally poorer memory performance compared with controls, while it was found to be impaired in patients with LTLE.

[Consistent Declarative Memory with Depressive Symptomatology]

INTRODUCTION

Some studies have suggested that potentiated remembrance of negative events on people with depressive disorders seems to be an important factor in the etiology, course and maintenance of depression.

OBJECTIVE

Evaluate the emotional memory in people with and without depressive symptomatology by means of an audio-visual test.

METHODOLOGY

73 university students were evaluated, male and female, between 18 and 40 years old, distributed in two groups: with depressive symptomatology (32) and without depressive symptomatology (40), using the Scale from the Center of Epidemiologic Studies for Depression (CES-D, English Abbreviation) and a cutting point of 20.

RESULTS

There were not meaningful differences between free and voluntary recalls, with and without depressive symptomatology, in spite of the fact that both groups had granted a higher emotional value to the audio-visual test and that they had associated it with emotional sadness.

CONCLUSION

People with depressive symptomatology did not exhibit the effect of mnemonic potentiation generally associated to the content of the emotional version of the test; therefore, the hypothesis of emotional consistency was not validated.

Distinct neural systems underlying reduced emotional enhancement for positive and negative stimuli in early Alzheimer's disease

Emotional information is typically better remembered than neutral content, and previous studies suggest that this effect is subserved particularly by the amygdala together with its interactions with the hippocampus. However, it is not known whether amygdala damage affects emotional memory performance at immediate and delayed recall, and whether its involvement is modulated by stimulus valence. Moreover, it is unclear to what extent more distributed neocortical regions involved in e.g., autobiographical memory, also contribute to emotional processing. We investigated these questions in a group of patients with Alzheimer's disease (AD), which affects the amygdala, hippocampus and neocortical regions. Healthy controls (n = 14), patients with AD (n = 15) and its putative prodrome amnestic mild cognitive impairment (n = 11) completed a memory task consisting of immediate and delayed free recall of a list of positive, negative and neutral words. Memory performance was related to brain integrity in region of interest and whole-brain voxel-based morphometry analyses. In the brain-behavioral analyses, the left amygdala volume predicted the immediate recall of both positive and negative material, whereas at delay, left and right amygdala volumes were associated with performance with positive and negative words, respectively. Whole-brain analyses revealed additional associations between left angular gyrus integrity and the immediate recall of positive words as well as between the orbitofrontal cortex and the delayed recall of negative words. These results indicate that emotional memory impairments in AD may be underpinned by damage to regions implicated in emotional processing as well as frontoparietal regions, which may exert their influence via autobiographical memories and organizational strategies.

Attentional capture by emotional stimuli is preserved in patients with amygdala lesions

The importance of cues signaling reward, threat or danger would suggest that they receive processing privileges in the neural systems underlying perception and attention. Previous research has documented enhanced processing of motivationally salient cues, and has pointed to the amygdala as a candidate neural structure underlying the enhancements. In the current study, we examined whether the amygdala was necessary for this emotional modulation of attention to occur. Patients with unilateral amygdala lesions and matched controls completed an emotional attentional blink task in which emotional distractors impair the perception of subsequent targets. Emotional images proved more distracting across all participant groups, including those with right or left amygdala lesions. These data argue against a central role for the amygdala in mediating all types of attentional capture by emotional stimuli.

Conscious and unconscious processing of fear after right amygdala damage: a single case ERP-study

In this study, we describe a 58-year-old male patient (FZ) with a right-amygdala lesion after temporal lobe infarction. FZ is unable to recognize fearful facial expressions. Instead, he consistently misinterprets expressions of fear for expressions of surprise. Employing EEG/ERP measures, we investigated whether presentation of fearful and surprised facial expressions would lead to different response patterns. We also measured ERPs to aversively conditioned and unconditioned fearful faces. We compared ERPs elicited by supraliminally and subliminally presented conditioned fearful faces (CS+), unconditioned fearful faces (CS-) and surprised faces. Despite FZ's inability to recognize fearful facial expressions in emotion recognition tasks, ERP components showed different response patterns to pictures of surprised and fearful facial expressions, indicating that covert or implicit recognition of fear is still intact. Differences between ERPs to CS+ and CS- were only found when these stimuli were presented subliminally. This indicates that intact right amygdala function is not necessary for aversive conditioning. Previous studies have stressed the importance of the right amygdala for discriminating facial emotional expressions and for classical conditioning. Our study suggests that the right amygdala is necessary for explicit recognition of fear, while implicit recognition of fear and classical conditioning may still occur following lesion of the right amygdala.

The Story Learning and Memory (SLAM) test: equivalence of three forms and sensitivity to left temporal lobe dysfunction

Remembering meaningful information is an important component of verbal memory. However, findings from existing story memory tests have been mixed in patients with temporal lobe epilepsy (TLE). We developed a test, the Story Learning and Memory (SLAM) test, in which a story is presented repeatedly until a performance criterion is reached, and verbatim recall is obtained only once, after a delay. In Study 1 we demonstrated a significant learning deficit in patients with left, but not right, TLE, and they were further impaired in retention of the story despite having learned it to the same criterion as subjects with right TLE and healthy subjects. These deficits remained confined to patients with left TLE after surgery. For clinical use we developed the SLAM in three versions in two languages; in studies 2 and 3 we tested and proved their equivalence.

Arousal enhanced memory retention is eliminated following temporal lobe resection

The amygdala, situated in the anterior medial temporal lobe (MTL), is involved in the emotional enhancement of memory. The present study evaluated whether anterior MTL-resections attenuated arousal induced memory enhancement for pictures. Also, the effect of MTL-resections on response latencies at retrieval was assessed. Thirty-one patients with unilateral MTL-resections (17 left, 14 right) together with 16 controls participated in a forced choice memory task with pictorial stimuli varying in arousal. Response latencies increased with stimulus arousal in controls but not in patients. This was paralleled by attenuated recognition memory for moderately and highly arousing pictures in MTL-resectioned patients as compared to healthy controls. However, patients and controls did not differ in memory performance for non-arousing pictures. These results suggest that the MTL is necessary for arousal induced memory enhancement.

Affective cognition and its disruption in mood disorders

In this review, we consider affective cognition, responses to emotional stimuli occurring in the context of cognitive evaluation. In particular, we discuss emotion categorization, biasing of memory and attention, as well as social/moral emotion. We discuss limited neuropsychological evidence suggesting that affective cognition depends critically on the amygdala, ventromedial frontal cortex, and the connections between them. We then consider neuroimaging studies of affective cognition in healthy volunteers, which have led to the development of more sophisticated neural models of these processes. Disturbances of affective cognition are a core and specific feature of mood disorders, and we discuss the evidence supporting this claim, both from behavioral and neuroimaging perspectives. Serotonin is considered to be a key neurotransmitter involved in depression, and there is a considerable body of research exploring whether serotonin may mediate disturbances of affective cognition. The final section presents an overview of this literature and considers implications for understanding the pathophysiology of mood disorder as well as developing and evaluating new treatment strategies.

Emotional declarative memory assessment of patients with mesial temporal lobe epilepsy and patients submitted to mesial temporal lobectomy

Epileptic seizures generate cognitive and behavioral impacts in individuals who suffer from epilepsy. Declarative memory is one of the cognitive functions that can be affected by epileptic seizures. The main objective of this work was to investigate neurocognitive function, especially the emotional working memory of patients with unilateral mesial temporal lobe epilepsy, and that of patients submitted to unilateral mesial temporal lobectomy. A face recognition test that can simultaneously recruit the frontal lobe (working memory) and mesial temporal lobe (emotional memory) was used to investigate emotional working memory. Our findings showed that the epilepsy factor significantly compromised the performance in the emotional memory test. On the other hand, surgical removal of the epileptic focus promoted an improvement in the emotional working memory of these patients, in addition to the significantly decrease in the number of seizures.

Functional imaging of emotional memory in bipolar disorder and schizophrenia

OBJECTIVES

Although in current diagnostic criteria there exists a distinction between bipolar disorder and schizophrenia, many patients manifest features of both disorders, and it is unclear which aspects, if any, confer diagnostic specificity. In the present study, we investigate whether there are differences in medial temporal lobe (MTL) activation in bipolar disorder and schizophrenia. We also investigate associations between activation levels and symptom severity across the disorders.

METHODS

Functional magnetic resonance imaging scans were conducted on 14 healthy controls, 14 patients with bipolar disorder, and 15 patients with schizophrenia undergoing an emotional memory paradigm.

RESULTS

All groups demonstrated the expected pattern of behavioural responses during encoding and retrieval, and there were no significant group differences in performance. Robust MTL activation was seen in all three groups during viewing of emotional scenes, which correlated significantly with recognition memory for emotional stimuli. The bipolar group demonstrated relatively greater increases in activation for emotional versus neutral scenes in the left hippocampus than both controls and patients with schizophrenia. There was a significant positive correlation between mania scores and activation in the anterior cingulate, and a significant negative correlation between depression scores and activation in the dorsolateral prefrontal cortex.

CONCLUSION

These results provide evidence that there are distinct patterns of activation in the MTL during an emotional memory task in bipolar disorder and schizophrenia. They also demonstrate that different mood states are associated with different neurobiological responses to emotion across the patient groups.

Verbal emotional memory in children and adolescents with temporal lobe epilepsy: a first study

That emotional memory enhancement is compromised in adult patients with temporal lobe epilepsy (TLE), particularly in the case of early cerebral damage, has been suspected. We conducted a study in which we compared 20 children and adolescents aged 11-15 years with early TLE with 40 healthy control subjects. We studied the effect of emotional information on verbal memory performance using story recall and word list learning tasks. Our results highlighted the existence of emotional memory facilitation in healthy subjects, whereas there was no beneficial impact of emotional material on memory in young patients with TLE. Our study suggests that early TLE can impair the development of emotional memory processes.

Emotional memory and migraine: effects of amitriptyline and sex related difference

Many studies suggest that emotional arousal improves memory storage. The aim of this study was to evaluate the effects of emotional content on explicit memory in untreated cephalalgic patients and in migraineurs treated with the antidepressant amitriptyline. We utilized an adaptation of two versions of the same story, with different arousing properties (neutral or emotional), which have been already employed in experiments involving the enhancing effects of emotions on memory retention. Subjects of the present study were healthy subjects and cephalalgic patients, suffering from migraine headache, which included untreated migraineurs and migraineurs treated with the antidepressant amitriptyline. The findings of our experiments suggest that chronic migraine is related to memory impairment. Taking into account that migraine is associated with major depression, in the present research the effect of the antidepressant amitriptyline was also evaluated. Our results showed that amitriptyline has an impairment effect on memory. In fact, the untreated migraineurs, compared to treated, recalled the most emotional phase of the arousal story significantly better. Then, our data suggest that amitriptyline prevents the enhancing effects of emotional content on memory processes. Moreover, in agreement with our previous data, this study suggests the existence of gender differences in the processing of emotional stimuli and underscores the importance of sex on emotional memory mechanisms.

Update on epilepsy and cerebral localization

The field of epilepsy has contributed significantly to localization of neurologic function, particularly in the neocortex. Methodologies such as cortical stimulation, positron emission tomography, functional MRI, trans-cranial magnetic stimulation, surgical resection, and magnetoencephalography have been used successfully in patients with epilepsy to locate specific functions, primarily for the purpose of defining eloquent cortex before surgical resections. The left hemisphere serves language-related functions and verbal memory in most people, whereas the right hemisphere serves some language function in addition to perceiving most components of music and other forms of nonverbal material. Both hemispheres cooperate in understanding spatial relationships. Studies in patients with developmental abnormalities have enriched our understanding of localization of function within the cortex. Future studies may help us understand the sequence in which specific regions are activated during specific tasks and determine which regions are necessary for tasks and which are supplementary. The ability to predict preoperatively the effect of removal of specific tissues would benefit surgical planning for all patients who undergo cortical resections, including those with epilepsy.

Emotional arousal enhances declarative memory in patients with Alzheimer's disease

OBJECTIVE

To verify whether the long-term retention of an emotionally arousing story is stronger than the retention of a neutral story, and the enhancing effects of emotional arousal on declarative memory in Alzheimer's disease (AD) patients.

METHOD

Twenty subjects (10 with AD and 10 controls matched for age and educational level) were studied. After the audiovisual presentation (neutral story), the subjects rated the narrative's emotionality. Later, they answered a multiple-choice questionnaire about the stories. Two weeks later, they watched the emotionally arousing story.

RESULTS

Subjects who watched the emotionally arousing story assigned a score of emotionality higher than the subjects in the neutral group (P = 0.023). In addition, the participants remembered more details of the arousing story, and had a higher score in the questionnaire (P < 0.001).

CONCLUSIONS

We demonstrated that an emotionally arousing content enhances long-term declarative memory in AD. Furthermore, present finding supports the use of this instrument for clinical and research purposes.

Sex-related lateralized effect of emotional content on declarative memory: an event related potential study

Several studies suggest that emotional arousal can promote memory storage. In this study, we evaluated the effects of emotional content on declarative memory, utilizing an adaptation of two versions of the same story, with different arousing properties (neutral or emotional), which have been already employed in experiments involving the enhancing effects of emotions on memory retention. We used event related potentials (ERP) to evaluate whether there is a sex-related hemispheric lateralization of electrical potentials elicited by the emotional content of a story. We compared left and right hemisphere P300 waves, recorded in P3 and P4 electrode sites, in response to emotional or neutral stimuli in men and women. In the left hemisphere, emotional stimuli elicited a stronger P300 in women, compared to men, as indexed by both amplitude and latency measures; moreover, the emotional content of the story elicited a stronger P300 in the right hemisphere in men than in women. The better memory for the arousal material may be related to the differential P300 at encoding. These data indicate that both sex and cerebral hemisphere constitute important, interacting influences on neural correlates of emotion, and of emotionally influenced memory.

The myth of silent cortex and the morbidity of epileptogenic tissue: implications for temporal lobectomy

This article reviews two commonly held myths regarding temporal lobe epilepsy-it is a static disorder with minimal morbidity and mortality, and epileptogenic tissue impairs only the functions of the seizure focus-and one myth concerning temporal lobe functions-they contain areas of nonfunctional, "silent" cortex. Chronic temporal lobe epilepsy can cause progressive structural, cognitive, and behavioral changes. Aside from the seizure focus, primary epileptogenic cortex may have a deleterious influence on distant brain areas. Removing this "nociferous" cortex and reducing the antiepileptic drug burden can improve cognitive or behavioral and metabolic function in areas remote from the resection. Anterior temporal lobectomy often removes functional tissue that may or may not be epileptogenic. Because normal brain does not contain functionless, "silent" areas, the procedure can have negative as well as positive cognitive or behavioral consequences. To improve the outcomes of focal cortical resections for seizure control, we need to better define functional and nociferous cortex and more clearly understand their boundaries and interactions.

The amygdala modulates the consolidation of memories of emotionally arousing experiences

Converging findings of animal and human studies provide compelling evidence that the amygdala is critically involved in enabling us to acquire and retain lasting memories of emotional experiences. This review focuses primarily on the findings of research investigating the role of the amygdala in modulating the consolidation of long-term memories. Considerable evidence from animal studies investigating the effects of posttraining systemic or intra-amygdala infusions of hormones and drugs, as well as selective lesions of specific amygdala nuclei, indicates that (a) the amygdala mediates the memory-modulating effects of adrenal stress hormones and several classes of neurotransmitters; (b) the effects are selectively mediated by the basolateral complex of the amygdala (BLA); (c) the influences involve interactions of several neuromodulatory systems within the BLA that converge in influencing noradrenergic and muscarinic cholinergic activation; (d) the BLA modulates memory consolidation via efferents to other brain regions, including the caudate nucleus, nucleus accumbens, and cortex; and (e) the BLA modulates the consolidation of memory of many different kinds of information. The findings of human brain imaging studies are consistent with those of animal studies in suggesting that activation of the amygdala influences the consolidation of long-term memory; the degree of activation of the amygdala by emotional arousal during encoding of emotionally arousing material (either pleasant or unpleasant) correlates highly with subsequent recall. The activation of neuromodulatory systems affecting the BLA and its projections to other brain regions involved in processing different kinds of information plays a key role in enabling emotionally significant experiences to be well remembered.