1,240 articles
Human Brain Project
The Human Brain Project was Europe's largest brain research initiative, running from 2013 to 2023 with a goal of simulating the human brain on a supercomputer.
Human echolocation
Human echolocation: using reflected sound, especially self-generated mouth clicks, to sense silent objects. Practiced by some blind people and trainable by sighted people; term coined 1944; 10-week training studies show broad learning.
Human eye
The human eye is the paired sensory organ that focuses light onto the retina, converting it into electrical signals sent through the optic nerve to the brain.
Huntington's disease
Huntington's disease (HD), also called Huntington's chorea, is an autosomal dominant neurodegenerative disease caused by CAG repeat expansion in the HTT gene, causing chorea, cognitive decline, and behavioral symptoms, typically starting in middle age with no cure.
Hyalocyte
Hyalocytes (of Hannover, Balazs) are yolk sac-derived resident macrophages of the eye's vitreous body, first identified in 1840, that maintain vitreous transparency, remodel the hyaloid vasculature, and drive proliferative vitreoretinal disease.
Hyperacusis
Hyperacusis is reduced tolerance to everyday sounds, perceived as too loud or painful despite normal hearing. Prevalence 9-15%; subtypes include loudness and pain hyperacusis; treated with sound desensitization and counseling.
Hypertensive retinopathy
Hypertensive retinopathy, also called fundus hypertonicus, is damage to the retinal blood vessels caused by high blood pressure, producing narrowed arterioles, hemorrhages, and exudates; treatment is mainly blood pressure control.
Hypertonia
Hypertonia, also called spasticity or rigidity in its main forms, is abnormally increased resistance to passive limb movement caused by loss of supraspinal control of stretch reflexes, assessed clinically with Ashworth and Tardieu scales.
Hyphema
Hyphema is blood in the eye's anterior chamber, usually from blunt trauma; graded 0–IV (microhyphema to eight-ball), complicated by rebleeding, raised intraocular pressure, and corneal blood staining.
Hypnic jerk
Hypnic jerk, also called sleep start or hypnagogic jerk: a brief involuntary myoclonic muscle contraction at sleep onset, stage N1, with falling sensation; affects about 70% of people, triggered by stress, caffeine, and sleep deprivation.
Hypogastric plexus
The hypogastric plexus is a network of nerve fibers in the pelvis, divided into superior and inferior parts, that supplies autonomic innervation to the bladder, rectum, and reproductive organs.
Hypoglossal nerve
Hypoglossal nerve (cranial nerve XII): pure motor nerve from the medulla's hypoglossal nucleus, exiting via the hypoglossal canal, supplying all tongue muscles except palatoglossus; lesions deviate the tongue toward the lesion.
Hypothalamic gonadotropin-releasing hormone neuron
Hypothalamic GnRH neuron, also called GnRH-1 neuron, a neuroendocrine cell born in the nasal placode that migrates into the forebrain and secretes pulsatile GnRH controlling LH/FSH release; its failure causes Kallmann syndrome and congenital hypogonadotropic hypogonadism.
Hypothalamus
Hypothalamus: small ventral brain region below the thalamus, about 2% of brain volume, controlling the pituitary via releasing hormones (TRH, GnRH, CRH, dopamine) and homeostasis, appetite, temperature, and circadian rhythm; mapped in 2025 as HYPOMAP with 452 cell types.
Hypotrichosis-deafness syndrome
Hypotrichosis-deafness syndrome, or hypotrichosis-hearing loss syndrome, is a rare autosomal dominant GJB2 (connexin 26) disorder with erythrokeratoderma, sparse hair, nail dystrophy, and sensorineural deafness.
Iatrogenic Creutzfeldt-Jakob disease
Iatrogenic Creutzfeldt-Jakob disease (iCJD): CJD acquired via contaminated medical treatment, mainly cadaveric growth hormone and dura mater grafts; under 1% of CJD cases, incubation up to decades.
Icteric sclera
Icteric sclera (scleral icterus, more accurately conjunctival icterus) is yellowing of the eye whites from excess bilirubin, appearing at roughly 2 to 3 mg/dL, an early sign of liver, biliary, or blood disease.
Idiopathic multifocal choroiditis
Idiopathic multifocal choroiditis (IMFC, ORPHA:714154) is a rare inflammatory white-dot chorioretinopathy of unknown cause, affecting young myopic white women, with punched-out lesions, frequent choroidal neovascularization, and steroid or immunosuppressive treatment.
Idiopathic posterior uveitis
Idiopathic posterior uveitis: inflammation of the retina or choroid with no identified infection, systemic disease, or defined syndrome after workup; 27-51% of US/European uveitis; treated with corticosteroids plus immunosuppression.
IIHTT trial
IIHTT (Idiopathic Intracranial Hypertension Treatment Trial, NCT01003639): NORDIC's 165-participant randomized trial showing acetazolamide plus a low-sodium weight-reduction diet modestly improved visual field, papilledema, quality of life, and weight in IIH with mild visual loss.
Impossible color
Impossible colors are color percepts, such as reddish green or the laboratory color olo, that no light spectrum can produce; they arise from opponent-process color coding or direct cone stimulation.
Inclusion body myopathy with Paget disease of bone and frontotemporal dementia
IBMPFD, now called multisystem proteinopathy (MSP1 when caused by VCP), is a rare autosomal dominant adult-onset disorder combining inclusion body myopathy, early Paget disease of bone, and frontotemporal dementia, with ALS and parkinsonism also in the spectrum.
Infectious epithelial keratitis
Infectious epithelial keratitis: rare, sight-threatening inflammation of the corneal epithelium from viral (mainly HSV-1), bacterial, fungal, or protist infection; dendritic ulcers; treated with oral acyclovir, valacyclovir, or topical antivirals.
Infectious intermediate uveitis
Infectious intermediate uveitis (ICD-11 9B66.1): infection-driven inflammation of the vitreous and peripheral retina, caused mainly by syphilis, tuberculosis, and Lyme disease, diagnosed by PCR, serology, and mNGS.
Infectious keratitis
Infectious keratitis, also called microbial or infective corneal ulcer, is corneal infection by bacteria, fungi, viruses, or Acanthamoeba; the leading cause of corneal blindness, diagnosed by scraping, culture, PCR, and confocal microscopy.
Inferior colliculus
The inferior colliculus (IC) is a paired midbrain structure serving as the main relay for auditory information traveling from the inner ear to the auditory cortex, supporting sound localization.
Inflammatory diseases of the retina
Inflammatory diseases of the retina (ICD-11 9B72, 網膜の炎症性疾患): retinal inflammation category covering viral retinitis (CMV, HIV) and unspecified forms; retinal vasculitis coded separately at 9B78.12.
Inherited retinal dystrophies
Inherited retinal dystrophies (IRDs), genetic retinal degenerations including retinitis pigmentosa, Stargardt disease, and Leber congenital amaurosis, affect about 1 in 3,000 people; over 350 genes are known, and Luxturna was the first approved gene therapy.
Inhibitory interneuron
Inhibitory interneurons are local-circuit neurons, mostly GABAergic (glycinergic in spinal cord), about 20% of cortical neurons, subdivided into PV, SOM, and 5HT3aR classes that stabilize networks, generate oscillations, and prevent epilepsy.
Inhibitory postsynaptic potential
Inhibitory postsynaptic potential (IPSP): hyperpolarizing or shunting postsynaptic response at GABA/glycine synapses, discovered by Eccles in 1952 in cat spinal motoneurons, driven by chloride and potassium conductances.