1,240 articles
Flavor
Flavor is the multisensory experience of eating, combining taste, retronasal smell, and trigeminal somatosensation, shaped by visual and sound cues; most people mistake it for taste alone and never notice the olfactory component.
Fleck corneal dystrophy
Fleck corneal dystrophy (FCD), or François-Neetens speckled corneal dystrophy, is a rare autosomal dominant PIKFYVE-related stromal corneal dystrophy with tiny non-progressive white flecks, normal vision, and no treatment required.
Floater
Floater (eye floater, myodesopsia): a dark spot, thread, or cobweb drifting across vision, caused by vitreous strands casting retinal shadows. Usually harmless; sudden new floaters with flashes signal possible retinal tear.
Floppy eyelid syndrome
Floppy eyelid syndrome (FES), also called lax eyelid condition-related syndrome, is an underdiagnosed eyelid laxity disorder with easy upper-lid eversion, chronic papillary conjunctivitis, and strong association with obesity and obstructive sleep apnea.
Floppy iris syndrome
Intraoperative floppy iris syndrome (IFIS), also called floppy iris syndrome, is a triad of billowing iris, iris prolapse, and progressive miosis during cataract surgery, strongly linked to tamsulosin (Flomax) use for benign prostatic hyperplasia.
Foix-Chavany-Marie syndrome
Foix-Chavany-Marie syndrome (FCMS), or bilateral anterior opercular syndrome, is a rare pseudobulbar palsy with anarthria, facio-pharyngo-glosso-masticatory paralysis, and preserved automatic movements, usually from bilateral opercular strokes.
Follicular conjunctivitis
Follicular conjunctivitis, ICD-11 9A60.1, is conjunctival inflammation with lymphoid follicles, usually viral (adenovirus) or chlamydial, sometimes toxic from eye drops; follicles distinguish it from papillary bacterial or allergic conjunctivitis.
Foot drop
Foot drop (drop foot): inability to lift the front of the foot, usually from peroneal nerve injury or L5 radiculopathy; managed with AFOs, functional electrical stimulation, physiotherapy, and tendon transfer surgery.
Foreign body in conjunctival sac
Foreign body in conjunctival sac (ICD-10 T15.1, ICD-11 ND70.1): external material such as dust, metal, or glass lodged in the conjunctival sac between eyeball and eyelids; removed by irrigation or moist cotton applicator after anesthetic.
Foreign body in ear
Foreign body in ear (ICD-11 ND71): an object lodged in the external auditory canal, common in children (beads, food, toys) and adults (insects, hearing aid parts). Button batteries are urgent; removal uses irrigation, suction, or instruments.
Foreign body on external eye
Foreign body on external eye (ICD-11 ND70): superficially adherent or embedded objects on the cornea or conjunctival sac, causing pain, tearing, and photophobia; managed by irrigation, swab, spud, or needle removal, antibiotics, and no patching.
Formication
Formication: tactile hallucination of insects crawling on or under the skin, from Latin formica (ant). Symptom of stimulant intoxication, menopause, neuropathy, and delusional infestation; not a delusion by itself.
Fracture of orbital floor
Fracture of orbital floor, or blowout fracture: break of the thin maxillary roof with intact inferior rim, causing diplopia, enophthalmos, and V2 numbness; repaired via transconjunctival, subciliary, subtarsal, or endoscopic approaches.
Free energy principle
Free energy principle (FEP), Karl Friston's theory of self-organizing biological agents: they minimize variational free energy, a bound on sensory surprise, via perception and active inference; corollary of Bayesian brain ideas, criticized as unfalsifiable.
Friedreich's ataxia
Friedreich's ataxia (FRDA) is an autosomal recessive ataxia from GAA repeat expansion in FXN causing frataxin deficiency; features gait ataxia, areflexia, cardiomyopathy, diabetes; omaveloxolone (Skyclarys) is the first approved drug.
Frontal lobe
Frontal lobe: anterior lobe of each cerebral hemisphere containing primary motor cortex, Broca's area, and prefrontal cortex; supports movement, expressive language, and divided prefrontal functions, not disproportionately enlarged in humans versus apes.
Frontal lobe disorder
Frontal lobe disorder, often called frontal lobe syndrome, is an impairment of brain function from damage to the frontal lobes, causing disinhibition, personality change, and impaired judgment.
Functional magnetic resonance imaging
Functional magnetic resonance imaging (fMRI), including BOLD task fMRI and resting-state fMRI, noninvasively maps brain activity via blood oxygenation; developed from Ogawa's 1990 BOLD discovery, used clinically for presurgical planning, with known poor task-fMRI test-retest reliability (mean ICC .397).
Functional near-infrared spectroscopy
Functional near-infrared spectroscopy (fNIRS), also called optical topography or diffuse optical imaging, is a portable, non-invasive neuroimaging method using 650–950 nm light to measure cortical HbO/HbR hemodynamic changes; first human studies 1991/1992, standardized by IEC 80601-2-71:2025.
Functional neuroimaging
Functional neuroimaging measures human brain activity via fMRI, PET, MEG, EEG, and fNIRS, either hemodynamically (millimeter spatial, seconds temporal) or electromagnetically (millisecond temporal), with clinical use in presurgical brain mapping.
Functional parkinsonism
Functional parkinsonism (FP), ICD-11 8A00.3, is a parkinsonian syndrome caused by functional neurological disorder, not dopamine degeneration; tremor, rigidity, and slowness show distractibility, entrainment, and no true bradykinesia.
Fungal keratitis
Fungal keratitis (mycotic keratitis, keratomycosis) is a fungal cornea infection causing blindness and eye loss, mainly from Fusarium, Aspergillus, and Candida after trauma or contact lens wear; treated with topical natamycin.
GABAergic interneuron
GABAergic interneuron: local inhibitory neuron using GABA as neurotransmitter, also called GABAergic inhibitory interneuron. Three cortical groups (PV ~40%, SST ~30%, 5HT3aR ~30%) arise from the ganglionic eminence and regulate circuit timing.
GABRB3
GABRB3, also called ECA5/DEE43, is a human gene at 15q12 encoding the beta3 subunit of the GABA_A inhibitory chloride-channel receptor. Pathogenic variants split into gain- and loss-of-function groups causing distinct epileptic encephalopathies; reduced expression marks Angelman and Prader-Willi syndromes.
Gallamine
Gallamine, marketed as the triethiodide salt Flaxedil, is a synthetic non-depolarizing neuromuscular blocking agent introduced in 1946 to relax skeletal muscle during general anesthesia, withdrawn after causing pronounced tachycardia.
Gamma motor neuron
A gamma motor neuron, also called a fusimotor neuron, is a lower motor neuron of the spinal cord or brainstem that innervates muscle spindle intrafusal fibers and regulates spindle sensitivity.
Gamma wave
Gamma wave: brain rhythm in the gamma band, roughly 30–90 Hz (definitions vary to 30–150 Hz), first named by Jasper and Andrews in 1938; generated by pyramidal cell–parvalbumin interneuron interactions, linked to attention, memory, and Alzheimer's research.
Gamut
Gamut: the subset of colors a device or color space (sRGB, Display P3, Rec. 2020) can represent; measured as coverage of a chromaticity triangle, distinct from color volume and accuracy.
Ganglionic eminence
The ganglionic eminence is a transient embryonic structure in the ventral telencephalon that produces the basal ganglia's neurons and most inhibitory interneurons of the cortex and hippocampus.
Gap junction
A gap junction, also known as a communicating junction or macula communicans, is a cluster of intercellular channels that lets ions and small molecules pass between cells.