Effects of normal aging and Alzheimer's disease on emotional memory

Recall is typically better for emotional than for neutral stimuli. This enhancement is believed to rely on limbic regions. Memory is also better for neutral stimuli embedded in an emotional context. The neural substrate supporting this effect has not been thoroughly investigated but may include frontal lobe, as well as limbic circuits. Alzheimer's disease (AD) results in atrophy of limbic structures, whereas normal aging relatively spares limbic regions but affects prefrontal areas. The authors hypothesized that AD would reduce all enhancement effects, whereas aging would disproportionately affect enhancement based on emotional context. The results confirmed the authors' hypotheses: Young and older adults, but not AD patients, showed better memory for emotional versus neutral pictures and words. Older adults and AD patients showed no benefit from emotional context, whereas young adults remembered more items embedded in an emotional versus neutral context.

The human amygdala: a systematic review and meta-analysis of volumetric magnetic resonance imaging

The structure and function of the human amygdala is attracting increasing attention in the scientific literature, particularly since the advent of high resolution magnetic resonance imaging (MRI). We carried out a systematic review of the published literature reporting left and right amygdala volumes from MRI in non-clinical subjects. Our aim was to estimate the normal range of the volume of the amygdala and to account for heterogeneity of the measures. The factors we considered included the detail given regarding various subject factors, the plane of scan acquisition, slice thickness and contiguity, magnet strength, positional and volume correction, and the reliability of measurement. Thirty-nine studies with 51 data sets fulfilled selection criteria. The mean+/-95% confidence interval for the left amygdala volume was 1726.7 mm(3)+/-35.1, and right was 1691.7 mm(3)+/-37.2. The left-right difference did not reach statistical significance. The overall range of reported volumes was 1050 mm(3) to 3880 mm(3). The amygdala is significantly larger in men and shows an inverse correlation with age. The main methodological factor found to influence amygdala measurement was anatomical definition. Studies using 'Watson's criteria' (Neurology 42 (1992) 1743) produced significantly larger volumes than the remainder. An index of study quality revealed an inverse relationship with volume-the higher the quality the smaller the volume. This reflected such factors as slice thickness, correction for brain volume, positional correction and number of subjects. We conclude by putting forward a detailed operationalized anatomical delineation of the amygdala, based on Watson's criteria. This work should guide future research in obtaining accurate and reliable amygdala volume measures which in turn will aid comparisons with clinical groups and the specification of structural-functional relationships.

Emotional memory and perception in temporal lobectomy patients with amygdala damage

BACKGROUND

The human amygdala is implicated in the formation of emotional memories and the perception of emotional stimuli--particularly fear--across various modalities.

OBJECTIVES

To discern the extent to which these functions are related.

METHODS

28 patients who had anterior temporal lobectomy (13 left and 15 right) for intractable epilepsy were recruited. Structural magnetic resonance imaging showed that three of them had atrophy of their remaining amygdala. All participants were given tests of affect perception from facial and vocal expressions and of emotional memory, using a standard narrative test and a novel test of word recognition. The results were standardised against matched healthy controls.

RESULTS

Performance on all emotion tasks in patients with unilateral lobectomy ranged from unimpaired to moderately impaired. Perception of emotions in faces and voices was (with exceptions) significantly positively correlated, indicating multimodal emotional processing. However, there was no correlation between the subjects' performance on tests of emotional memory and perception. Several subjects showed strong emotional memory enhancement but poor fear perception. Patients with bilateral amygdala damage had greater impairment, particularly on the narrative test of emotional memory, one showing superior fear recognition but absent memory enhancement.

CONCLUSIONS

Bilateral amygdala damage is particularly disruptive of emotional memory processes in comparison with unilateral temporal lobectomy. On a cognitive level, the pattern of results implies that perception of emotional expressions and emotional memory are supported by separate processing systems or streams.

A prospective study of the effects of anterior temporal lobectomy on emotion recognition and theory of mind

Nineteen patients evaluated facial emotional expressions and performed 'theory of mind' reasoning tasks before and after a temporal lobectomy for medically intractable epilepsy, and results were compared with the performance of 19 healthy controls. Following operation, which in all cases resulted in excision of the entire amygdala, there was no change in the ability to reason about the mental states of others, in line with the suggestion that the anterior temporal lobe is not necessary for theory of mind reasoning. However, following a left anterior temporal lobectomy, patients evaluated fearful facial expressions in a more normative manner. This may reflect the excision of a 'hyper-excitable' amygdala which pre-operatively misinterprets fearful expressions as containing blends of other emotions. Alternatively the results may represent an improvement in function of the right amygdala following the excision of a noxious inhibitory epileptogenic focus on the left. The finding complements earlier demonstrations that damage to the right amygdala is associated with impaired processing of fear; amelioration of right amygdala function may conversely be associated with an improvement.

Emotional memory in depersonalization disorder: a functional MRI study

This study examines emotional memory effects in primary depersonalization disorder (DPD). A core complaint of DPD sufferers is the dulling of emotional responses, and previous work has shown that, in response to aversive stimuli, DPD patients do not show activation of brain regions involved in normal emotional processing. We hypothesized that DPD sufferers would not show the normal emotional enhancement of memory, and that they would not show activation of brain regions concerned with emotional processing during encoding and recognition of emotional verbal material. Using fMRI, 10 DPD patients were compared with an age-matched healthy control group while performing a test of emotional verbal memory, comprising one encoding and two recognition memory tasks. DPD patients showed significantly enhanced recognition for overtly emotive words, but did not show enhancement of memory for neutral words encoded in an emotive context. In addition, patients did not show activation of emotional processing areas during encoding, and exhibited no substantial difference in their neural responses to emotional and neutral material in the encoding and emotional word recognition tasks. This study provides further evidence that patients with DPD do not process emotionally salient material in the same way as healthy controls, in accordance with their subjective descriptions of reduced or absent emotional responses.

Emotional memory: separating content and context

It is now well established that emotion enhances episodic memory. However, it remains unclear whether the same neural processes underlie enhancement of memory for both emotional stimuli and neutral stimuli encoded in an emotive context. We designed an experiment that specifically attempted to separate these effects and that was validated on 30 participants. We then used functional magnetic resonance imaging (fMRI) to examine the neural correlates of encoding and retrieval of the two classes of stimuli in 12 healthy male volunteers. We predicted that aversive emotional context would enhance memory regardless of content and that activation of anterior cingulate would be inversely related to retrieval of aversive items. Both predictions were supported. Furthermore we demonstrated apparent asymmetrical lateralisation of activation in the hippocampal/parahippocampal complex during recognition of words from aversive sentences: more left-sided activation for neutral words from aversive contexts, and more right-sided activation for aversive content words. These findings, if applicable to the wider population, may have application in a range of psychiatric disorders where interactions between emotion and cognition are relevant.

Relationship between post-operative depression/anxiety and hippocampal/amygdala volumes in temporal lobectomy for epilepsy

PURPOSE

Patients with temporal lobe epilepsy (TLE) often present mood disturbances, which may either exacerbate or remit following surgery. The objective of the study was to investigate the relationship between post-operative depressive/anxiety symptoms and hippocampal/amygdala volumes following anterior temporal lobectomy.

METHODS

Thirty-five patients operated for TLE were assessed for mood disturbances by the Beck depression inventory (BDI) and Beck anxiety inventory (BAI). Post-operative MRI data were collected and volumetric analysis of the hippocampi (HV) and amygdala (AV) was performed. Correlations between volumetric data, measures of mood, and demographic and clinical data were calculated.

RESULTS

BDI scores significantly correlated with the intact HV (p=0.029) as well as the absolute difference between the intact and remnant HV (p=0.021). This was evident in left-side resections (p=0.049); in right-side resections the correlation was marginally non- significant (p=0.057). Depressed patients also had smaller remnant AV (p=0.002). Furthermore, BAI was negatively correlated with the HV remnant in left-side resections (p=0.038). No other significant associations between post-operative mood disturbances and various demographic and clinical variables were observed.

CONCLUSION

The severity of depressive symptomatology in operated epilepsy patients correlates with the extent of hippocampal and amygdala resection; this association appears to be more evident in left-side resections.

Quantitative magnetic resonance imaging of the amygdala in temporal lobe epilepsy-clinico-pathological correlations (a pilot study)

PURPOSE

We carried out a pilot study of quantitative volumetric MRI of the amygdala in patients undergoing surgery for intractable temporal lobe epilepsy. We wished to explore whether amygdala volume correlated with pre-operative clinical variables and post-operative outcome.

METHODS

Ten patients had detailed volumetric measurements of their amygdala and hippocampus according to operationalised anatomical criteria from an optimised MRI imaging sequence. A ratio of volumes from the unoperated to operated side was calculated. Surgical specimens were examined histologically for astrocytosis.

RESULTS

The volumes of the amygdala and hippocampus on the operated side were significantly smaller than on the unoperated side. More severe astrocytosis appeared to go along with smaller volume ratios but the relationship was not significant. There were few significant correlations between volumes measures and clinical or outcome variables.

CONCLUSION

Reductions in amygdala volume in the to-be-operated temporal lobe in patients with medically intractable epilepsy can be reliably detected using volumetric MRI. Accurate amygdala volume measures do not appear to exert a significant effect on clinical presentation and outcome in the presence of hippocampal volumes reductions, but may be useful in confirming bilateral pathology. Larger studies examining clinico-pathological correlations are recommended.

A critical period for the impact of amygdala damage on the emotional enhancement of memory?

The amygdala is crucial in modulating enhanced memory for emotionally arousing material. The authors provide evidence that unilateral lesions of the human amygdala arising early in development, but not in adulthood, are associated with a loss of the expected superior retrieval of emotionally arousing over neutral material. This adds to evidence for an early critical period in the development of amygdala function.

Priority water research questions as determined by UK practitioners and policy makers

Several recent studies have emphasised the need for a more integrated process in which researchers, policy makers and practitioners interact to identify research priorities. This paper discusses such a process with respect to the UK water sector, detailing how questions were developed through inter-disciplinary collaboration using online questionnaires and a stakeholder workshop. The paper details the 94 key questions arising, and provides commentary on their scale and scope. Prioritization voting divided the nine research themes into three categories: (1) extreme events (primarily flooding), valuing freshwater services, and water supply, treatment and distribution [each >150/1109 votes]; (2) freshwater pollution and integrated catchment management [100-150 votes] and; (3) freshwater biodiversity, water industry governance, understanding and managing demand and communicating water research [50-100 votes]. The biggest demand was for research to improve understanding of intervention impacts in the water environment, while a need for improved understanding of basic processes was also clearly expressed, particularly with respect to impacts of pollution and aquatic ecosystems. Questions that addressed aspects of appraisal, particularly incorporation of ecological service values into decision making, were also strongly represented. The findings revealed that sustainability has entered the lexicon of the UK water sector, but much remains to be done to embed the concept operationally, with key sustainability issues such as resilience and interaction with related key sectors, such as energy and agriculture, relatively poorly addressed. However, the exercise also revealed that a necessary condition for sustainable development, effective communication between scientists, practitioners and policy makers, already appears to be relatively well established in the UK water sector.