Barbara Brierley

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.

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 for words: Separating content and context

We developed a technique to examine the effects of emotional content and context on verbal memory. Two sets of sentences were devised: in the first, each sentence was emotionally arousing due to the inclusion of an emotional “target” word. In the second set, “targets” were replaced with well-matched neutral words. Subjects read aloud a selection of emotional and neutral sentences, and were then surprised with memory tasks after a range of time delays. Emotional target words were remembered significantly better than neutral words in all experiments. Recognition of emotional words was relatively stable despite increasing delays between encoding and recognition testing, in contrast to memory for neutral words, which decayed over time. Memory for neutral non-target words was enhanced when words had been presented in an emotional context. The results confirm the phenomenon of emotional enhancement of memory at short and long delays and suggest that emotional context may be encoded independently of word meaning.

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.