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Glossary 479pulsatile cerebral blood flow, and the maintenance of uniform pressure within thebrain and spinal cord.Cyclothymia A chronic, low-level form of bipolar disorder that consists of shortperiods of mild depression alternating with short periods of hypomania.Declarative memory The aspect of memory that stores facts, objects, and eventsand can be divided into two types: episodic, or knowledge about events in aperson’s past, and semantic, or knowledge of the meaning of words. Can be contrastedwith procedural memory, which stores skills and operations.Decussation The crossing of a neuronal pathway from one side of the body tothe contralateral side.Depolarization Excitation or decrease in the membrane potential of the postsynapticcell increasing the likelihood that a neuron will generate an action potential.Dexamethasone challenge A procedure designed to assess function of the hypothalamicpituitary adrenal axis; involves the administration of the synthetic steroid,dexamethasone, followed by measurement of cortisol levels to obtain thetest results.d fenfluramine challenge A procedure in which d fenfluramine stimulates therelease of serotonin and acts as a potent inhibitor of the reuptake of serotonin intothe nerve terminal. The prolactin response to d fenfluramine challenge has been usedto assess serotonergic function and appears to be blunted in depressed patients.Diffusion tensor imaging An MRI based technique that allows the visualizationof location, orientation, and the anisotropy (being directionally dependent orhaving different characteristics depending on the specific direction) of the brain’swhite matter tracts.Dopamine A catecholamine neurotransmitter found abundantly in the brain; isthought to play a role in Parkinson’s disease and has important functions in thelearning of novel stimuli, the experience of pleasure, the development of substanceabuse and in the neural functioning of psychosis.Dopamine receptors A class of metabotropic G protein-coupled receptors withdopamine as their endogenous ligand.D1-like receptor Members of this family include the D1 and D5 dopamine receptorsthat tend to have excitatory actions.