Behavioral Neuroscience: Homeostasis, Learning and Memory, and Circadian Rhythms

Comprehensive vocabulary flashcards covering the homeostatic regulation of temperature and fluid balance, synaptic and behavioral mechanisms of learning and memory, and the neurobiology of circadian rhythms and sleep stages.

Homeostasis

The physiological process by which the body regulates its internal environment to maintain a stable, relatively constant condition, characterized by a set point, detection mechanisms for deviations, and internal or behavioral effectors to restore balance.

Negative Feedback Loop

A homeostatic regulatory mechanism in which a stimulus-induced deviation triggers a response that counteracts and inhibits the original change, returning physiological levels to the set point.

Set Point

The target or ideal physiological value within a homeostatic system around which normal fluctuations occur and from which deviations trigger compensatory responses.

Endotherm

An organism (such as a mammal or bird) that generates internal metabolic heat to maintain a constant internal core body temperature independent of external environmental temperatures.

Ectotherm

An organism (such as a reptile or amphibian) whose body temperature fluctuates with and depends largely on the temperature of the surrounding environment.

Vasodilation

The widening of blood vessels in the skin, which increases blood flow to the surface to promote heat dissipation into the environment during warm conditions.

Vasoconstriction

The narrowing of cutaneous blood vessels to divert blood away from peripheral skin capillaries toward core organs, minimizing convective heat loss under cold conditions.

Raynaud's Phenomenon

An atypical vascular condition marked by excessive vasospasm of small blood vessels in extremities upon cold exposure, turning skin white due to lack of blood flow, then blue due to lack of oxygen, and red upon reperfusion.

Transient Receptor Potential (TRP) Channels

A family of ion channel thermoreceptors in sensory neurons responsive to specific temperature ranges, including TRPA1 (cold-pain), TRPM8 (cold), TRPV4 and TRPV3 (warm), and TRPV1 and TRPV2 (heat-pain).

Preoptic Area (POA)

An anterior hypothalamic region containing warm-sensitive neurons that integrate peripheral and central thermal information to coordinate heat-loss responses such as vasodilation and sweating.

Posterior Hypothalamus

The hypothalamic brain region crucial for coordinating heat-conservation and heat-production responses, such as shivering, piloerection, and peripheral vasoconstriction during cold exposure.

Hypothermia

A dangerous physiological condition occurring when core body temperature drops below $95^\circ\text{F}$ ($35^\circ\text{C}$), resulting from prolonged cold exposure, exhaustion, or impaired thermoregulation.

Heat Stroke

A severe, life-threatening hyperthermic emergency where body temperature exceeds $104^\circ\text{F}\text{--}105^\circ\text{F}+$ accompanied by central nervous system dysfunction such as confusion, slurred speech, unconsciousness, and cessation of sweating.

Pyrogens

Fever-producing substances (such as bacterial endotoxins or pro-inflammatory cytokines IL-1, TNF, IL-6) that trigger increased $PGE_2$ synthesis to raise the hypothalamic thermal set point.

Antipyretics

Anti-fever medications that reduce body temperature by inhibiting cyclooxygenase (COX) enzymes, interrupting the synthesis of prostaglandin $E_2$ ($PGE_2$) to restore the normal hypothalamic set point.

Intracellular Fluid (ICF)

The fluid compartment contained entirely within cells, comprising approximately $67\%$ of the body's total water volume and characterized by high concentrations of potassium ($K^+$) ions.

Extracellular Fluid (ECF)

The fluid outside of cells, representing about $33\%$ of the body's water, divided into interstitial fluid ($26\%$), blood plasma ($7\%$), and CSF ($<1\%$), rich in sodium ($Na^+$) and chloride ($Cl^-$) ions.

Osmosis

The passive net movement of water molecules through a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Median Preoptic Nucleus (MnPO)

A key hypothalamic integrative drinking center whose glutamate-producing neurons stimulate voracious drinking behavior when activated, whereas its GABA-producing neurons terminate drinking.

Prandial Thirst

The anticipated consumption of liquids occurring during meal consumption to assist in mastication, swallowing, and gastrointestinal digestion.

Osmotic Thirst

Thirst triggered by cellular dehydration when high extracellular solute concentrations (such as sodium or sugar) draw water out of intracellular compartments via osmosis.

Hypovolemic Thirst

Thirst elicited by a reduction in total blood volume or interstitial fluid volume resulting from fluid loss such as hemorrhage, vomiting, diarrhea, or excessive sweating.

Organum Vasculosum of the Lamina Terminalis (OVLT)

A circumventricular organ adjacent to the third ventricle that lacks a blood-brain barrier and contains central osmoreceptors that detect cellular dehydration and project to the MnPO.

Baroreceptors

Mechanoreceptor sensory neurons located in the carotid sinus, aortic arch, heart, and kidneys that fire action potentials in response to blood vessel stretch to monitor blood pressure and volume.

Antidiuretic Hormone (ADH)

A peptide hormone (also called vasopressin) synthesized by the hypothalamus and released by the posterior pituitary to signal renal tubules to conserve water and concentrate urine.

Aldosterone

A steroid hormone released by the adrenal cortex in response to angiotensin II that acts on the kidneys to promote the retention of sodium ($Na^+$) and conservation of fluid volume.

Hyponatremia

A dangerous physiological condition characterized by abnormally low sodium levels in extracellular fluid, often caused by excessive water intake ('water intoxication'), leading to cellular swelling and cerebral edema.

Mehandru/Vachharajani Syndrome

A seizure disorder identified by researchers caused by acute, severe hyponatremia triggered by the excessive overconsumption of hard seltzers.

Habituation

A form of non-associative learning where the magnitude or frequency of a behavioral response progressively decreases following repeated exposure to a non-threatening stimulus.

Sensitization

A form of non-associative learning characterized by an enhanced behavioral response to a mild or moderate stimulus following prior exposure to a noxious or highly salient stimulus.

Aplysia californica

A marine sea slug utilized by Eric Kandel as a model organism to dissect the neural and molecular circuitry underlying non-associative learning through its defensive gill-withdrawal reflex.

Habituation in Aplysia

A homosynaptic depression mechanism wherein repeated mechanical stimulation of the siphon results in decreased neurotransmitter release from the sensory neuron presynaptic terminal onto the motor neuron.

Sensitization in Aplysia

A heterosynaptic facilitation process where tail shock activates facilitating interneurons that release serotonin onto sensory axon terminals, increasing neurotransmitter release and producing stronger gill withdrawal.

Classical Conditioning

An associative learning paradigm where an unconditioned stimulus (US) that reliably evokes an unconditioned response (UR) is paired with a neutral conditioned stimulus (CS) until the CS alone elicits a conditioned response (CR).

Operant Conditioning

An associative learning form wherein voluntary behaviors are strengthened through positive or negative reinforcement or weakened through punishment based on their consequences.

Information Processing Model of Memory

A structural framework dividing memory into sensory memory ($1\text{--}2\,\text{seconds}$, large capacity), short-term memory ($15\text{--}18\,\text{seconds}$, $5\text{--}9\,\text{items}$), and long-term memory (indefinite duration, unlimited capacity).

Working Memory

A multicomponent short-term memory system comprising a central executive, visuospatial sketchpad, episodic buffer, and phonological loop that actively manipulates information over several seconds.

Episodic Memory

A subtype of explicit declarative memory involving the autobiographical recollection of specific personal events and experiences tied to a particular spatial and temporal context.

Semantic Memory

A subtype of explicit declarative memory encompassing general knowledge about the world, concepts, language, facts, and word meanings without reference to personal experience.

Procedural Memory

A form of nondeclarative (implicit) memory supporting the automatic acquisition and performance of motor and cognitive skills and behavioral habits without conscious recall.

Delay Conditioning

A classical conditioning protocol where the conditioned stimulus (CS) is presented and remains on until the unconditioned stimulus (US) is delivered, overlapping in time and ending together; mediated predominantly by the cerebellum.

Trace Conditioning

A classical conditioning protocol where the CS terminates before the US begins, separated by a stimulus-free trace interval; dependent on the cerebellum, hippocampus, and prefrontal cortex.

Purkinje Cells

Large, flat GABAergic cerebellar cortex neurons with elaborate two-dimensional dendritic arbors that receive sensory inputs from parallel fibers and climbing fibers, providing tonic inhibition to deep cerebellar nuclei.

Lateral Interpositus Nucleus (LIP)

A deep cerebellar nucleus essential for learning and executing the conditioned eyeblink response; disinhibited when Purkinje cells undergo long-term depression (LTD).

Lateral Nucleus of the Amygdala (LA)

The primary sensory input hub of the amygdala that integrates auditory CS (tone) and somatosensory US (shock) inputs and undergoes long-term potentiation during auditory fear conditioning.

Central Nucleus of the Amygdala (CE)

The major amygdalar output nucleus that receives processed information from the lateral nucleus and projects to the brainstem and hypothalamus to drive defensive fear responses like freezing and autonomic activation.

Mirror Neurons

Neurons in the frontal-parietal mirror neuron system (including premotor cortex, inferior frontal gyrus, and inferior parietal lobule) that fire both when an individual executes an action and when observing another individual perform that same action.

Hebb Rule

The neurophysiological postulate proposed by Donald Hebb (1949) stating that when two interconnected neurons are repeatedly activated together, the synaptic connection between them is strengthened ('cells that fire together, wire together').

Long-Term Potentiation (LTP)

A persistent, activity-dependent increase in synaptic strength following high-frequency electrical stimulation (tetanus), requiring glutamate binding to AMPA and NMDA receptors and postsynaptic $Ca^{2+}$ influx.

Long-Term Depression (LTD)

An activity-dependent decrease in synaptic efficacy resulting from prolonged low-frequency stimulation, leading to a modest intracellular $Ca^{2+}$ rise and the internalization/removal of postsynaptic AMPA receptors.

NMDA Receptor

A glutamate-gated ionotropic receptor blocked at resting membrane potentials by magnesium ($Mg^{2+}$); upon postsynaptic depolarization, $Mg^{2+}$ is expelled, allowing calcium ($Ca^{2+}$) to enter and activate intracellular protein kinases.

Patient H.M. (Henry Molaison)

A famous neurological patient who underwent bilateral medial temporal lobe resection (including hippocampi) in 1953 by William Scoville to treat intractable epilepsy, resulting in profound anterograde amnesia with preserved procedural memory.

Anterograde Amnesia

The inability to encode, consolidate, or form new explicit declarative memories for events, facts, or people encountered after the onset of brain injury or surgical trauma.

Retrograde Amnesia

The loss of memories for events and information that were acquired prior to the onset of neurological injury, often exhibiting a temporal gradient where older memories remain better preserved.

Perforant Pathway

The major sensory projection tract carrying axonal fibers from the entorhinal cortex through the subiculum to synapse on granule cells within the dentate gyrus of the hippocampal formation.

Circadian Rhythm

An endogenous physiological or behavioral cycle of approximately 24 hours that persists even in the complete absence of external environmental time cues.

Chronotype

An individual's innate behavioral manifestation and preference for timing sleep and peak alertness, varying across phenotypes such as early birds (morning larks), hummingbirds, and night owls.

Zeitgeber

An external environmental cue (German for 'time giver'), primarily sunlight, that entrains and synchronizes an organism's biological circadian clock to the 24-hour solar day.

Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs)

Specialized non-image-forming photoreceptive retinal ganglion cells that express the photopigment melanopsin and project directly to the suprachiasmatic nucleus via the retinohypothalamic tract.

Melanopsin

A photopigment present within ipRGCs maximally sensitive to blue light wavelengths (approximately $480\text{--}500\,\text{nm}$) that mediates circadian photic entrainment rather than visual perception.

Retinohypothalamic Tract

A monosynaptic neural pathway that originates from ipRGCs in the retina and projects directly to the suprachiasmatic nucleus (SCN) of the hypothalamus to convey environmental light levels.

Suprachiasmatic Nucleus (SCN)

The master circadian pacemaker in mammals, situated directly above the optic chiasm in the anterior hypothalamus, that maintains endogenous 24-hour rhythmic gene expression to drive subordinate physiological oscillators.

SCN Transplantation Experiments

Landmark studies by Ralph et al. (1990) showing that transplanting fetal SCN tissue into SCN-lesioned arrhythmic hamsters restored circadian locomotor rhythms matching the endogenous cycle length of the donor genotype.

Melatonin

A hormone synthesized and secreted by the pineal gland exclusively during darkness that signals nighttime to bodily organs and helps initiate the opening of the sleep gate.

Free-Running Rhythm

A natural biological rhythm that operates independently of all external cyclic zeitgebers, which averages approximately 25 hours in humans placed under constant ambient conditions.

Phase Advance

A circadian shift requiring sleep and wake times to occur earlier in the cycle (analogous to eastward travel or 'Spring Forward'), which is physiologically harder to adjust to than phase delay.

Phase Delay

A circadian shift requiring sleep and wake times to occur later in the cycle (analogous to westward travel or 'Fall Back'), which is physiologically easier to adapt to because human endogenous rhythms exceed 24 hours.

Electroencephalogram (EEG) Rhythms

Extracellular recordings of synchronized post-synaptic potentials across cortical pyramidal neurons categorized into frequency bands: Delta ($1\text{--}4\,\text{Hz}$), Theta ($4\text{--}8\,\text{Hz}$), Alpha ($8\text{--}12\,\text{Hz}$), Beta ($13\text{--}30\,\text{Hz}$), and Gamma ($30\text{--}100+\,\text{Hz}$).

NREM Stage 1 (N1)

The initial light sleep transition stage comprising approximately $5\%$ of sleep, characterized by the emergence of theta rhythms and occasional sudden muscle contractions known as hypnic jerks.

Hypnic Myoclonia

A brief, involuntary muscle twitch (also called a 'hypnic jerk') that occurs during the initial transition into sleep (Stage N1), often triggered by a vestibular misinterpretation of falling.

NREM Stage 2 (N2)

A light sleep stage accounting for $45\text{--}55\%$ of total adult sleep, characterized by the hallmark presence of sleep spindles (bursts of $12\text{--}14\,\text{Hz}$ activity) and high-voltage K-complexes.

Sleep Spindles

Short bursts of high-frequency ($12\text{--}14\,\text{Hz}$) brainwave activity originating from thalamocortical loops during Stage N2 sleep that aid in sensory gating and memory consolidation.

K-Complexes

Sharp, high-voltage biphasic EEG waveforms occurring approximately once per minute during Stage N2 sleep, either spontaneously or in response to subtle external acoustic stimuli.

NREM Stage 3 (N3)

Slow-wave deep sleep (SWS) characterized by high-amplitude, low-frequency delta waves ($1\text{--}4\,\text{Hz}$), parasympathetic dominance, growth hormone secretion, and high arousal thresholds.

Glymphatic System

A glial-dependent convective waste-clearance pathway in the brain that expands during NREM Stage 3 sleep, utilizing cerebrospinal fluid influx to flush out toxic metabolites including beta-amyloid.

Rapid Eye Movement (REM) Sleep

A paradoxical sleep stage characterized by low-voltage desynchronized beta/theta-like EEG activity, bursts of rapid eye movements, autonomic arousal, vivid narrative dreams, and generalized skeletal muscle atonia.

Muscle Atonia

The temporary flaccid paralysis of somatic muscles during REM sleep resulting from inhibitory cholinergic projections from the rostral pons activating glycine and GABAergic spinal motor interneurons.

REM Sleep Behavior Disorder (RBD)

A parasomnia marked by the neurological failure to inhibit spinal motor circuits during REM sleep, causing individuals to violently act out vivid, frightening dreams; strongly associated with alpha-synucleinopathies like Parkinson's disease.

Locus Coeruleus (LC)

A noradrenergic brainstem nucleus in the pons that promotes alert wakefulness through wide cortical projections, exhibiting reduced firing in NREM sleep and complete silence during REM sleep.

Raphe Nuclei

A series of serotonergic brainstem nuclei that promote wakefulness, decrease activity during NREM sleep, and fall virtually quiescent during REM sleep.

Rostral Pons

The cholinergic REM-ON center of the brainstem that triggers the characteristic signs of REM sleep, including cortical desynchrony, rapid eye movements, and active motor inhibition.

Adenosine

An endogenous somnogen that progressively accumulates in the basal forebrain and cortex during prolonged wakefulness to create homeostatic sleep pressure; competitively antagonized by caffeine.

Narcolepsy

A chronic sleep disorder characterized by excessive daytime sleepiness, sudden sleep attacks, microsleeps, and intrusion of REM phenomena directly into wakefulness, linked to the autoimmune loss of hypocretin (orexin) neurons in the lateral hypothalamus.

Cataplexy

A sudden, episodic loss of voluntary muscle tone and postural control triggered by strong emotions (such as laughter, surprise, or anger) seen in narcolepsy, reflecting sudden daytime REM atonia.

Activation-Synthesis Theory

A neurobiological model proposing that dreams represent the forebrain's attempt to synthesize and weave a coherent narrative out of random cholinergic pontine-geniculate-occipital (PGO) neural bursts generated during REM sleep.