Neuroscience
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Obsessive Compulsive Disorder (OCD) is a common neuropsychiatric disorder with unknown molecular underpinnings. Identification of genetic and non-genetic risk factors has largely been elusive, primarily because of a lack of power. In contrast, neuroimaging has consistently implicated the cortico-striatal-thalamo-cortical circuits in OCD. ⋯ Construct validity is more difficult to establish in the context of a limited understanding of OCD risk factors. Our current models may help us to dissect the circuits and molecular pathways that can elicit OCD-relevant behavior in rodents. We can hope that this growing understanding, coupled with developing technology, will prepare us when robust OCD risk factors are better understood.
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Cognitive flexibility, the ability to adjust behavior in response to new and unexpected conditions in the environment, is essential for adaptation to new challenges and survival. The cholinergic system is an important modulator of this complex behavior however, the exact cholinergic circuits involved in this modulation and the precise influence of acetylcholine (ACh) in the process is still not fully understood. Here we review the role of different cholinergic circuits in cognitive flexibility. ⋯ We highlight the fact that when investigating effects of ACh on behavioral flexibility, or any other behavior, one has to keep in mind two important particularities of the cholinergic system: (1) Many cholinergic neurons in the brain co-release glutamate or GABA with ACh. Methodologies that rely on neuronal silencing or ablation lead to simultaneous elimination of both neurotransmitters, making interpretation of results complex. (2) The cholinergic gene locus has a unique organization, with the vesicular acetylcholine transporter (VAChT) gene present within the intron between the first and second exons of the choline acetyltransferase (ChAT) gene. Thus, behavioral studies using transgenic animals generated with ChAT bacterial artificial chromosome (BAC) clones should be considered carefully, taking into consideration that these mice may overexpress VAChT and therefore, present a hypercholinergic tone that can be a confounder in behavioral studies.
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Schizophrenia (SZ) has long been associated with a variety of cognitive deficits, including reduced cognitive flexibility. More recent findings, however, point to tremendous inter-individual variability among patients on measures of cognitive flexibility/set-shifting. With an eye toward shedding light on potential sources of variability in set-shifting abilities among SZ patients, I examine the neural substrates of underlying probabilistic reversal learning (PRL) - a paradigmatic measure of cognitive flexibility - as well as neuromodulatory influences upon these systems. Finally, I report on behavioral and neuroimaging studies of PRL in SZ patients, discussing the potentially influences of illness profile and antipsychotic medications on cognitive flexibility in SZ.
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Anxiety often is studied as a stand-alone construct in laboratory models. But in the context of coping with real-life anxiety, its negative impacts extend beyond aversive feelings and involve disruptions in ongoing goal-directed behaviors and cognitive functioning. Critical examples of cognitive constructs affected by anxiety are cognitive flexibility and decision making. ⋯ The brain region most critically involved in behavioral flexibility is the prefrontal cortex (PFC), but little is known about how anxiety impacts PFC encoding of internal and external events that are critical for flexible behavior. Here we review animal and human neurophysiological and neuroimaging studies implicating PFC neural processing in anxiety-induced deficits in cognitive flexibility. We then suggest experimental and analytical approaches for future studies to gain a better mechanistic understanding of impaired cognitive inflexibility in anxiety and related disorders.
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To adaptively respond in a complex, changing world, animals need to flexibly update their understanding of the world when their expectations are violated. Though several brain regions in rodents and primates have been implicated in aspects of this updating, current models of orbitofrontal cortex (OFC) and norepinephrine neurons of the locus coeruleus (LC-NE) suggest that each plays a role in responding to environmental change, where the OFC allows updating of prior learning to occur without overwriting or unlearning one's previous understanding of the world that changed, while elevated tonic NE allows for increased flexibility in behavior that tracks an animal's uncertainty. In light of recent studies highlighting a specific LC-NE projection to the OFC, in this review we discuss current models of OFC and NE function, and their potential synergy in the updating of associations following environmental change.