Håkan Fischer

A functional MRI study of human amygdala responses to facial expressions of fear versus anger.

Functional magnetic resonance imaging (fMRI) of the human brain was used to compare changes in amygdala activity associated with viewing facial expressions of fear and anger. Pictures of human faces bearing expressions of fear or anger, as well as faces with neutral expressions, were presented to 8 healthy participants. The blood oxygen-level dependent (BOLD) fMRI signal within the dorsal amygdala was significantly greater to Fear versus Anger, in a direct contrast. Significant BOLD signal changes in the ventral amygdala were observed in contrasts of Fear versus Neutral expressions and, in a more spatially circumscribed region, to Anger versus Neutral expressions. Thus, activity in the amygdala is greater to fearful facial expressions when contrasted with either neutral or angry faces. Furthermore, directly contrasting fear with angry faces highlighted involvement of the dorsal amygdaloid region.

Differential prefrontal cortex and amygdala habituation to repeatedly presented emotional stimuli.

Repeated presentations of emotional facial expressions were used to assess habituation in the human brain using fMRI. Significant fMRI signal decrement was present in the left dorsolateral prefrontal and premotor cortex, and right amygdala. Within the left prefrontal cortex greater habituation to happy vs fearful stimuli was evident, suggesting devotion of sustained neural resources for processing of threat vs safety signals. In the amygdala, significantly greater habituation was observed on the right compared to the left. In contrast, the left amygdala was significantly more activated than the right to the contrast of fear vs happy. We speculate that the right amygdala is part of a dynamic emotional stimulus detection system, while the left is specialized for sustained stimulus evaluations.

Gender and age differences in the prevalence of specific fears and phobias

Point prevalence of specific fears and phobias was determined in 704 respondents of 1000 randomly selected adults aged 18-70 yr. A phobia for lightning, enclosed spaces, darkness, flying, heights, spiders, snakes, injections, dentists and/or injuries was defined if subjects reported a fear that was out of conscious control, interfered with life and lead to the avoidance of the feared object [American Psychiatric Association, 1994. Diagnostic and statistical manual of mental disorders (4th edn). Washington, DC: American Psychiatric Press.] Fear intensity was assessed using visual analogue scales. A factor analysis generally supported the classification of fears and phobias into: (1) situational phobias (lightning, enclosed spaces, darkness, flying and heights); (2) animal phobias (spiders and snakes); and (3) mutilation phobias (injections, dentists, injuries). Total point prevalence of any specific phobia was 19.9% (26.5% for females and 12.4% for males). In total, 21.2% women and 10.9% men met criterias for any single specific phobia. Multiple phobias was reported by 5.4% of the females and 1.5% of the males. Animal phobia had a prevalence of 12.1% in women and 3.3% in men. Point prevalence of situational phobia was 17.4% in women and 8.5% in men. For mutilation phobia no gender difference was observed, being presented in 3.2% of the women and 2.7% of the men. Women as compared to men gave higher fear ratings for all objects and situations. Inanimate object fears and phobias were more common in older than younger individuals. Animal fears were more intense in younger than in older individuals. Fear of flying increased and fear of injections decreased as a function of age in women but not in men. Thus, specific fears and phobias are heterogeneous with respect to sex and age distribution.

Differential response in the human amygdala to racial outgroup vs ingroup face stimuli.

Here we describe response in the human amygdala to the presentation of racial outgroup vs ingroup faces. Functional magnetic resonance imaging (fMRI) measures of brain activity were acquired while subjects who identified themselves as White or Black viewed photographs of both White and Black faces. Across all subjects, we observed significantly greater blood oxygen-level-dependent (BOLD) signal in the amygdala to outgroup vs ingroup faces, but only during later stimulus presentations. A region of interest (ROI)-based analysis of these voxels revealed a significant interaction between amygdala response to outgroup and ingroup faces over time. Specifically, the greater amygdala activation to outgroup faces during later stimulus presentations was the result of amygdala response habituation to repeated presentations of ingroup faces with sustained responses to outgroup faces. The present results suggest that amygdala responses to human face stimuli are affected by the relationship between the perceived race of the stimulus face and that of the subject. Results are discussed as consistent with a role for the amygdala in encoding socially and/or biologically relevant information. We conclude that researchers seeking to study brain responses to face stimuli in human subjects should consider the relationship between the race of subjects and stimuli as a significant potential source of variance. Moreover, these data provide a foundation for future related studies in the neuroscience of social cognition and race.

Brain habituation during repeated exposure to fearful and neutral faces: a functional MRI study.

Central nervous system habituation in humans was studied using functional magnetic resonance imaging and repeated presentations of single fearful and neutral faces. Habituation of blood-oxygenation-level-dependent (BOLD) signal during exposure to face stimuli, collapsed over fearful and neutral expressions, was evident in the right amygdala and hippocampus, as well as in the medial/inferior temporal cortex bilaterally. In the hippocampus, significantly greater habituation was evident on the right as compared to the left side, which could reflect the visual nature of the stimuli. There were no time by expression interaction effects in these regions, suggesting similar neural attenuation rates to fearful and neutral face stimuli. These results indicate that brain regions involved in novelty detection and memory processing habituate at similar rates regardless of whether the face in focus displays an aversive emotional expression or not.

Neurofunctional correlates of posttraumatic stress disorder: A PET symptom provocation study.

Summary Patients with combat-related posttraumatic stress disorder (PTSD) show altered cognitive and affective processing and symptomatic responding following exposure to trauma reminders. Previous symptom provocation studies using brain imaging have involved Vietnam veterans. In this study neural correlates were investigated in patients with PTSD resulting from trauma in more recent war zones. 15Oxygen water and positron emission tomography were used to measure regional cerebral blood flow (rCBF) in patients with war- and combat-related chronic PTSD during exposure to combat and neutral sounds. Self-reports and heart rate confirmed symptomatic responding during traumatic stimulation. The war-related condition, as compared to the neutral, increased rCBF in the right sensorimotor areas (Brodmann areas 4/6), extending into the primary sensory cortex (areas 1/2/3), and the cerebellar vermis. RCBF also increased in the right amygdala and in the periaqueductal gray matter adjacent to the pons. During provocation rCBF was lowered in the right retrosplenial cortex (areas 26/29/30 extending into area 23). Symptom provocation in PTSD promote sensorimotor, amygdaloid and midbrain activation. We conclude that perceptually induced symptom activation in PTSD is associated with an emotionally determined motor preparation and propose that subcortically initiated rather than cortically controlled memory mechanisms determine this pattern.

The amygdala and individual differences in human fear conditioning.

WHILE animal research on fear conditioning suggests crucial involvement of the amygdala, this has not been corroborated in humans when using subtractive neuro-imaging methodology. Correlation analyses might be more able to reveal relations between individual differences in conditionability and central neural activity. Hence, we performed a directed search for amygdalar participation in human fear conditioning by correlating central and autonomic nervous activity. [15O]Butanol positron emission tomography evaluated regional cerebral blood flow (rCBF) in six subjects before and after aversive conditioning to visual snake stimuli. Nonspecific electrodermal fluctuations (EDA) were recorded simultaneously. A significant positive correlation was obtained between conditioned EDA and conditioned rCBF in the right amygdala (r = 0.75, p < 0.05), supporting involvement of the amygdala in human fear conditioning.

Functional neuroanatomical correlates of electrodermal activity: A positron emission tomographic study

To reveal areas in the central nervous system of importance for electrodermal control, regional cerebral blood flow (rCBF) was correlated to nonspecific skin conductance fluctuations (NSF) during aversive and nonaversive conditions. Participants viewed a TV screen displaying white noise or snake videotapes presented both with and without electric shocks given to the right hand. H2 15 O positron emission tomography was used to measure rCBF, and the constant voltage technique was used to measure NSF from the left hand. Electrodermal activity was positively related to rCBF in the left primary motor cortex (MI, Brodmanns Area 4) and bilaterally in the anterior (Areas 24 and 32) and posterior cingulate cortex (Area 23). Negative relations were observed bilaterally in the secondary visual cortex (Areas 18 and 19) and the right inferior parietal cortex (Area 39), with a tendency also for the right insular cortex (Areas 13, 15, and 16). Because results from lesion and stimulation studies in humans converge with the present imaging results, we conclude that the cingulum and the motor cortex, in addition to the parietal and possibly the insular cortex, form part of one or several distributed neural network(s) involved in electrodermal control. Because these areas also support anticipation, affect, and locomotion, electrodermal responses seem to reflect cognitively or emotionally mediated motor preparation.

Neural correlates of training-related working-memory gains in old age

Working memory (WM) functioning declines in old age. Due to its impact on many higher-order cognitive functions, investigating whether training can modify WM performance has recently been of great interest. We examined the relationship between behavioral performance and neural activity following five weeks of intensive WM training in 23 healthy older adults (M=63.7 years). 12 participants received adaptive training (i.e. individually adjusted task difficulty to bring individuals to their performance maximum), whereas the others served as active controls (i.e. fixed low-level practice). Brain activity was measured before and after training, using fMRI, while subjects performed a WM task under two difficulty conditions. Although there were no training-related changes in WM during scanning, neocortical brain activity decreased post training and these decreases were larger in the adaptive training group than in the controls under high WM load. This pattern suggests intervention-related increases in neural efficiency. Further, there were disproportionate gains in the adaptive training group in trained as well as in non-trained (i.e. attention, episodic memory) tasks assessed outside the scanner, indicating the efficacy of the training regimen. Critically, the degree of training-related changes in brain activity (i.e. neocortical decreases and subcortical increases) was related to the maximum gain score achieved during the intervention period. This relationship suggests that the decreased activity, but also specific activity increases, observed were functionally relevant.

Affective and attentive neural networks in humans: a PET-study of pavlovian conditioning.

Using positron emission tomography (PET) and [15O]butanol we studied regional cerebral blood flow (rCBF) to a visual snake stimulus before and after classical conditioning with an unconditioned electric shock delivered to the right hand. Measures of heart rate, electrodermal activity, state anxiety and subjective distress confirmed classical conditioning of physiological and subjective responses. Subcortically, conditioning increased rCBF bilaterally in the ventromedial thalamus, the posterior hypothalamus and the central grey of the midbrain. Cortically, rCBF increased in the left anterior and posterior cingulate gyrus, the left primary somatosensory cortex, the left premotor cortex and bilaterally in parietal areas. Thus, the functional organization of classical conditioning in humans involves autonomic, affective and attentive brain mechanisms.