Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item INTERACTIONS BETWEEN APPETITIVE AND AVERSIVE PROCESSING DURING PERCEPTION AND ATTENTION(2017) Padmala, Srikanth; Pessoa, Luiz; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although understanding brain mechanisms of appetitive-aversive interactions is relevant to our daily lives and has potential clinical relevance, our knowledge about these brain mechanisms is rudimentary. To address this gap in the literature, we conducted two functional MRI studies that investigated appetitive-aversive interactions during perception and attention in healthy adult human brain. In the first study, we probed how potential reward signaled by advance cues altered aversive distractor processing during a subsequent visual task. Behaviorally, the deleterious influence of aversive stimuli on task performance was reduced during the reward compared to no-reward condition. In the brain, at the task phase, paralleling the observed behavioral pattern, significant interactions were observed in the anterior insula and dorsal anterior cingulate cortex, such that responses during the negative (vs. neutral) condition were reduced during the reward compared to no-reward condition. Notably, negative distractor processing in the amygdala appeared to be independent of the reward manipulation. During the initial cue phase, we observed increased reward-related responses in the ventral striatum, which were correlated with behavioral interference scores at the subsequent task phase, revealing that participants with increased reward-related responses exhibited a greater behavioral benefit of reward in reducing the adverse effect of negative images. Furthermore, the ventral striatum exhibited stronger functional connectivity with fronto-parietal regions important for attentional control. These findings contribute to the understanding of how potential reward influences attentional control and reduces negative distractor processing in the human brain. In the second study, we investigated brain mechanisms underlying the joint processing of positive and negative emotional information during a passive viewing task. Specifically we focused on probing the pattern of appetitive-aversive interactions in brain regions sensitive to the valence and salience of emotional stimuli. In a subset of regions that were sensitive to stimulus valence, competitive interaction patterns were observed. Notably, in other valence-coding regions such as the ventro-medial prefrontal cortex no evidence for competitive interactions was detected. Conversely, in regions sensitive to salience, cooperative interaction patterns were observed. The findings of competitive and cooperative type interactions supported contextual modulation of emotional processing in the human brain.Item CHOLINERGIC CONTRIBUTIONS TO EMOTION REGULATION(2004-12-17) Benson, Brenda Ellen; Cohen, Avis H; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Theories based on clinical and neuroanatomical studies implicate the muscarinic cholinergic system in normal and pathological emotion regulation. Emotional and sensory experiences can be induced with intravenous administration of the local anesthetic procaine hydrochloride, which selectively activates limbic regions in humans and animals. Procaine has a high affinity for muscarinic cholinergic receptors in vitro. This research tests three hypotheses: (1) procaine binds to muscarinic receptors in vivo; (2) procaine alters functional connectivity among cholinergic brain regions and their targets; and (3) procaine-induced emotions are related to core cholinergic regions. In Experiment I, anesthetized rhesus monkeys underwent positron emission tomography (PET) studies before and after administration of six doses of procaine on separate days using a radioligand with preferential binding to muscarinic M2 receptors ([18F]FP-TZTP). Procaine blocked [18F]FP-TZTP in a dose-response fashion uniformly across the brain, while significantly increasing tracer flow in limbic compared with non-limbic regions. In Experiment II, behavioral and physiological measures were assessed at baseline and following procaine in 32 healthy controls and 15 patients with bipolar disorder undergoing [15O] PET yielding regional cerebral blood flow (rCBF). Procaine selectively increased rCBF in anterior paralimbic regions in healthy controls, but to a lesser degree in patients. Regions connected via cholinergic pathways showed significantly different functional connectivity in both groups with procaine, however, prefrontal regions showed differential functional connectivity with cholinergic brain regions in patients compared with controls. Changes in activity of cholinergic regions explained the variance in anxiety ratings in an opposite manner in each group, and in euphoria ratings only in patients. In conclusion, procaine binds directly with muscarinic receptors in vivo while selectively increasing limbic activity in anesthetized monkeys. Two key findings herein procaine-induced alterations in functional connectivity of core cholinergic regions in humans, and the association of core cholinergic regional activity with emotional experience support theories implicating cholinergic contributions to emotion regulation. Decreased anterior paralimbic activity and altered functional connectivity of cholinergic regions in patients with bipolar illness compared with controls revealed by procaine offers additional insight into the regional neurobiology of the disease, and may ultimately be targeted in therapeutic approaches to bipolar disorder.