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Background and purpose
The insula has important functions in monitoring and integrating physiological responses to a personal experience of multimodal input. The experience of chills in response to auditory stimuli is an important example for a relevant arousing experience coupled with bodily response. A group study about altered chill experiences in patients with insula lesions is lacking.
Methods
Twenty-eight stroke patients with predominantly insula lesions in the chronic stage and 14 age-matched controls were investigated using chill stimuli of both valences (music, harsh sounds). Group differences were analyzed in subjective chill reports, associated bodily responses (skin conductance response), lesion mapping, diffusion-weighted imaging and functional magnetic resonance imaging. Other neuropsychological deficits were excluded by comprehensive testing. Diffusion-weighted imaging was quantified for four insula tracts using fractional anisotropy.
Results
The frequency of chill experiences was comparable between participant groups. However, bodily responses were decreased for the stroke group. Whereas there was no association of lesion location, a positive association was found for the skin conductance response during aversive sounds and the tract connecting anterior inferior insula and left temporal pole in the stroke group. Similarly, functional magnetic resonance imaging activation in areas hypothesized to compensate for damage was increased with bodily response.
Conclusions
A decoupling of felt arousal and bodily response after insula lesion was observed. Impaired bodily response was related to an impaired interaction of the left anterior insula and the temporal pole.
Chills are emotional peaks especially in response toward acoustic stimuli. In the present study, we examined facial expressions associated with pleasant and unpleasant chill experiences during music and harsh sounds by measuring electromyographic activity from facial corrugator and zygomatic muscles. A rubber bulb could be pressed by the participants to report chill intensities. During harsh sounds, increased activation of both corrugator and zygomatic muscle was observed. Zygomatic muscle activity was even more pronounced when a chill experience was reported during such sounds. In contrast, pleasant chill experiences during music were associated with slightly increased corrugator activity compared with absent chills. Our data suggest that harsh sounds produce a painful facial expression that is even intensified when a chill experience is reported. Increased corrugator activity during chills toward music might refer to states of being moved. The results are discussed in the light of a proposed role of the chill in regulating social behavior. Our results suggest that recording facial muscle activity can be a valuable method for the examination of pleasant and unpleasant peak emotions induced by acoustic stimuli.
Our emotional experiences depend on our interoceptive ability to perceive and interpret changes in our autonomous nervous system. An inaccurate perception and interpretation of autonomic changes impairs our ability to understand and regulate our emotional reactions. Impairments in emotion understanding and emotion regulation increase our risk for mental disorders, indicating that interoceptive deficits play an important role in the etiology and pathogenesis of mental disorders. We, thus, need measures to identify those of us whose interoceptive deficits impair their emotion understanding and emotion regulation. Here, we used cardiac measures to investigate how our ability to engage prefrontal and (para-)limbic brain region regions affects our ability to perceive and interpret cardiac changes. We administered a heartbeat detection task to a sample of healthy individuals (n = 113) whose prefrontal-(para-) limbic engagement had been determined on basis of a heart rate variability recording. We found a positive association between heartbeat detection and heart rate variability, implying that individuals with higher heart rate variability were more accurate in heartbeat detection than individuals with lower heart rate variability. These findings suggest that our interoceptive accuracy depends on our prefrontal-(para-)limbic engagement during the perception and interpretation of cardiac changes. Our findings also show that cardiac measures may be useful to investigate the association between interoceptive accuracy and prefrontal-(para-)limbic engagement in a time- and cost-efficient manner.
There is multiple evidence that emotionally arousing events are preferentially processed, and better remembered than neutral events. In the present dissertation I investigated whether those strong emotional memories are affected by acute and chronic stress. Moreover, I was interested in whether already established emotional memories can be changed by behavioral intervention. According to the modulation hypothesis, emotionally arousing events promote attention and memory processes via noradrenergic and glucocorticoid actions. Recent models suggest that stress hormones differentially impact mnemonic processing, namely encoding, (re-) consolidation and memory retrieval, depending on timing and duration of the stressor relative to the learning experience. Acute stress around the time of encoding has been found to enhance memory, whereas chronic stress has been associated with memory impairments. Furthermore, consolidated memories are not resistant to modifications. Following reactivation, memories can turn into an unstable state and undergo a process called reconsolidated in order to persist. During this vulnerable state, memories are prone to modification, for instance by pharmacological blockade or interference learning. Here, the modulation of newly formed emotional and neutral memories as well as existing emotional and neutral memories was investigated in a well-established picture viewing and recognition memory paradigm using behavioral and neurophysiological measures (event-related potential, ERPs). More elaborative processing of emotional, relative to neutral stimuli has been related to the late positive potential (LPP). During encoding of emotional and neutral pictures, enhanced LPPs (starting at about 400 ms after stimulus onset) are usually observed for emotionally arousing relative to neutral pictures, indicating preferential attention allocation and processing. During recognition, correctly recognized old items evoke larger ERP amplitudes than correctly identified new items. This difference, the ERP old/new effect, was used to measure mnemonic processing during retrieval. The ERP old/new effect over centro-parietal sensor sites (400-800 ms) has been associated with recollection processes, and is enhanced for emotional, compared to neutral materials. Three studies are presented, that investigated 1) the influence of acute stress prior to encoding on long-term memory and its neural correlates, 2) the impact of chronic stress on encoding and memory, and 3) the influence of interference on already established memories (reconsolidation), always contrasting emotionally arousing and neutral scenes. Study 1 investigated subsequent recognition memory after encoding following acute stress using a socially evaluated cold pressure test, while study 2 tested the influence of chronic stress investigating breast cancer survivors about two years after cancer treatment. In study 3, one day after encoding, reconsolidation of the reactivated picture memory was targeted with an interfering learning task. In all three studies, recognition memory was tested one week later. High-density electroencephalograms (EEGs; 257 electrodes) were recorded to measure brain potentials. The results showed, in line with previous research, that emotionally arousing scenes were preferentially processed, as indicated by larger LPPs, and were better remembered than neutral scenes, as indicated by enhanced memory performance and larger ERP old/new differences. Experiencing acute stress prior to encoding enhanced the centro-parietal ERP old/new effect for emotionally arousing pictures at recognition, corroborating that acute stress facilitates memory for emotional scenes (Study 1). In contrast, attenuated LPPs for unpleasant pictures and impaired memory performance for arousing pictures were observed in breast cancer survivors (Study 2), indicating altered attention to emotion and subsequent emotional memory storage in chronically stressed individuals. When memory reactivation was followed by an interfering learning task, recognition memory and ERP old/new differences were attenuated for emotionally arousing scenes, selectively, showing the possibility that emotional memories might be modulated by behavioral interventions (Study 3). The results of all three studies are discussed and integrated into a model of memory modulation by stress and interference. The results highlight the importance of understanding the role of emotional arousal in the processes of memory formation, retrieval and reconsolidation. Moreover, shedding light on the differential effects of acute and chronic stress, interference and their possible interactions might help to prevent and even modify impairing memories that are one of the major concerns in stress- and fear-related mental disorders.