Nicholas Medford

Time courses of left and right amygdalar responses to fearful facial expressions.

Despite the many studies highlighting the role of the amygdala in fear perception, few have examined differences between right and left amygdalar responses. Using functional magnetic resonance imaging (fMRI), we examined neural responses in three groups of healthy volunteers (n = 18) to alternating blocks of fearful and neutral faces. Initial observation of extracted time series of both amygdalae to these stimuli indicated more rapid decreases of right than left amygdalar responses to fearful faces, and increasing magnitudes of right amygdalar responses to neutral faces with time. We compared right and left responses statistically by modeling each time series with (1) a stationary fit model (assuming a constant magnitude of amygdalar response to consecutive blocks of fearful faces) and (2) an adaptive model (no assumptions). Areas of significant sustained nonstationarity (time series points with significantly greater adaptive than stationary model fits) were demonstrated for both amygdalae. There was more significant nonstationarity of right than left amygdalar responses to neutral, and left than right amygdalar responses to fearful faces. These findings indicate significant variability over time of both right and left amygdalar responses to fearful and neutral facial expressions and are the first demonstration of specific differences in time courses of right and left amygdalar responses to these stimuli. Hum. Brain Mapping 12:193–202, 2001.

Deriving meaning: Distinct neural mechanisms for metaphoric, literal, and non-meaningful sentences

In this study, we used a novel cognitive paradigm and event-related functional magnetic resonance imaging (ER-fMRI) to investigate the neural substrates involved in processing three different types of sentences. Participants read either metaphoric (Some surgeons are butchers), literal (Some surgeons are fathers), or non-meaningful sentences (Some surgeons are shelves) and had to decide whether they made sense or not. We demonstrate that processing of the different sentence types relied on distinct neural mechanisms. Activation of the left inferior frontal gyrus (LIFG), BA 47, was shared by both non-meaningful and metaphoric sentences but not by literal sentences. Furthermore, activation of the left thalamus appeared to be specifically involved in deriving meaning from metaphoric sentences despite lack of reaction times differences between literals and metaphors. We assign this to the ad hoc concept construction and open-endedness of metaphoric interpretation. In contrast to previous studies, our results do not support the view the right hemispheric is specifically involved in metaphor comprehension.

Depersonalization disorder: thinking without feeling

Patients with depersonalization disorder (DP) experience a detachment from their own senses and surrounding events, as if they were outside observers. A particularly common symptom is emotional detachment from the surroundings. Using functional magnetic resonance imaging (fMRI), we compared neural responses to emotionally salient stimuli in DP patients, and in psychiatric and healthy control subjects. Six patients with DP, 10 with obsessive-compulsive disorder (OCD), and six volunteers were scanned whilst viewing standardized pictures of aversive and neutral scenes, matched for visual complexity. Pictures were then rated for emotional content. Both control groups rated aversive pictures as much more emotive, and demonstrated in response to these scenes significantly greater activation in regions important for disgust perception, the insula and occipito-temporal cortex, than DP patients (covarying for age, years of education and total extent of brain activation). In DP patients, aversive scenes activated the right ventral prefrontal cortex. The insula was activated only by neutral scenes in this group. Our findings indicate that a core phenomenon of depersonalization--absent subjective experience of emotion--is associated with reduced neural responses in emotion-sensitive regions, and increased responses in regions associated with emotion regulation.

How metaphors influence semantic relatedness judgments: The role of the right frontal cortex

We used event-related fMRI (ER-fMRI) to test the hypothesis that metaphors bias cognitive processing of semantic relatedness towards a search for a wider range of associations. Twelve right-handed male volunteers read a mixture of metaphoric and literal sentences, each sentence being followed by a single word, which could be semantically related or not to the preceding sentence context. We found that judging unrelated words as contextually irrelevant was associated with increased blood oxygenation level-dependent (BOLD) signal in the right ventrolateral prefrontal cortex in the metaphoric but not in the literal condition. The same region was also activated when subjects endorsed a semantic relation between words and metaphoric sentence primes but not between words and literal sentence primes. We argue that these results are consistent with the notion of semantic open-endedness, whereby figurative statements bias cognitive processing towards a search for a wider range of semantic relationships compared to literal statements, and thus lend further support to the view that coarse semantic coding occurs preferentially in the right hemisphere.

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.

Empathy and enduring depersonalization: The role of self-related processes

Abstract Empathy has two key components: affective and cognitive. It relies on “embodied” processes such as the generation, representation and perception of feeling states. People diagnosed with Depersonalization Disorder (DPD) report disturbances in affective experience, such as emotional numbing, alongside aberrations in “body image” such as increased self-focus and feelings of “disembodiment”. DPD therefore provides a test bed for the role of such self-related processes in empathy. We tested 16 participants diagnosed with DPD and 48 control volunteers on measures of cognitive and affective empathy. We used self-report measures (EQ; Baron-Cohen & Wheelwright, 2004), an objective measure of cognitive empathy—the “Eyes” task (Baron-Cohen, Wheelwright, Hill, Raste, & Plumb, 2001), and a novel task tapping affective empathy, utilizing speech rate as an implicit measure of physiological arousal. We also measured participants’ tendency to use mental representations that relate to the self during the affective empathy task. The DPD group showed intact performance on the cognitive empathy task. However, there was a disruption in the physiological component of affective empathy alongside a more pronounced reliance on mental representations of the self. These findings suggest affective empathy to be reliant on intact emotional experience in the observer. In addition, excessive self-focus may be detrimental to an empathic response.