1,240 articles
Injectable bioelectronic mesh
Injectable bioelectronic mesh is a flexible, biocompatible electronic mesh injected through a syringe needle that unfurls inside soft tissue to record from or stimulate many neurons.
Injury of axillary nerve
Injury of axillary nerve: damage to the C5-C6 posterior cord branch supplying deltoid and teres minor, usually from anterior shoulder dislocation or proximal humeral fracture; mostly non-operative recovery, surgery if no recovery by 3-6 months.
Injury of cauda equina
Injury of cauda equina (ICD-11 NB72): damage to the lumbosacral nerve roots below the conus medullaris, causing lower motor neuron deficits, saddle sensory loss, and bladder, bowel, and sexual dysfunction; traumatic and compressive causes, treated by urgent decompression.
Injury of facial nerve
Injury of facial nerve: damage to cranial nerve VII causing facial weakness or paralysis, from trauma (3% of facial palsy cases), surgery, infection, or Bell palsy; graded by House-Brackmann scale.
Injury of lens
Injury of lens is trauma to the crystalline lens of the eye, including traumatic cataract, subluxation, and dislocation, and a leading cause of vision impairment after ocular trauma.
Injury of oculomotor nerve
Injury of oculomotor nerve (ICD-11 NA04.2) is damage to cranial nerve III, causing oculomotor nerve palsy with down-and-out eye deviation, ptosis, diplopia, and sometimes pupil dilation; causes include microvascular disease, aneurysm, tumor, and head trauma.
Injury of the auricle
Injury of the auricle (ICD-11 NA0B): trauma to the external ear's cartilaginous pinna, including hematoma, laceration, avulsion, and fracture; key risks are cauliflower ear deformity, chondritis, and the need for prompt drainage or specialist repair.
Injury of vagus nerve
Injury of the vagus nerve (CN X), usually surgical, causing vocal fold paralysis with hoarseness and dysphagia; prognosis assessed by laryngeal electromyography, most recovery within 6 months.
Inner ear
Inner ear (labyrinth): cochlea for hearing and vestibular system for balance, in the temporal bone's bony labyrinth with perilymph and membranous labyrinth with endolymph; hair cells transduce sound and head motion via tip-linked MET channels.
Instinct
Instinct: unlearned, inherited, species-typical behavior, also called innate behavior. Traced from Darwin and James through McDougall, the 1920s critiques (Dunlap, Kuo), ethology's fixed action patterns, and Lehrman's critique.
Insular cortex
Insular cortex (insula, Island of Reil): cortical region hidden in the lateral sulcus, first described by Reil in 1809; hub for interoception, emotion, salience network, cognitive control, and social cognition.
Integrated information theory
Integrated information theory (IIT), proposed by Giulio Tononi in 2004, identifies consciousness with integrated information measured by Φ, with versions 3.0 and 4.0, a clinical proxy (PCI), critiques by Aaronson and a 124-signer pseudoscience letter, and mixed 2025 adversarial-collaboration results.
Interaural time difference
Interaural time difference (ITD): the arrival-time difference of a sound at the two ears, the dominant cue for horizontal sound localization at low frequencies, encoded by coincidence-detecting MSO neurons, with human sensitivity near 10 microseconds and a maximum near 763 microseconds.
Intercostal nerves
Intercostal nerves (nervi intercostales) are the anterior rami of thoracic spinal nerves T1-T11 running in the costal grooves; T7-T11 continue as thoracoabdominal nerves, T12 is the subcostal nerve, and T2 gives the intercostobrachial nerve.
Internal capsule
The internal capsule (capsula interna) is a compact band of white matter in each cerebral hemisphere where a small stroke can paralyze the opposite side of the body.
International Brain Research Organization
The International Brain Research Organization (IBRO), founded in 1961 with UNESCO support, is a global federation of neuroscience societies that funds training, exchanges, and collaborative research, especially in economically disadvantaged countries.
International Spinal Cord Society
International Spinal Cord Society (ISCoS), formerly International Medical Society of Paraplegia, founded 1961 by Ludwig Guttmann at Stoke Mandeville, renamed 2001; professional society for spinal cord injury care, research, and the Annual Scientific Meeting.
Interneuron
Interneuron: a neuron that is neither motor nor sensory; commonly, a local GABAergic inhibitory cell of the cortex and hippocampus, about 20% of cortical neurons, with PV, SST, and 5HT3aR subgroups and links to epilepsy, schizophrenia, and autism.
Interplexiform cell
Interplexiform cell (IPC), a retinal amacrine-cell subtype or separate class with processes in both inner and outer plexiform layers; coined by Gallego 1971; carries one-way centrifugal feedback from inner to outer retina via dopaminergic, GABAergic, or glycinergic synapses.
Intervertebral foramen
Intervertebral foramen (foramen intervertebrale, neural foramen): opening between adjacent vertebrae linking the spinal canal to the extraspinal region; bounded by pedicles, disc, and facet capsule; transmits spinal nerves and vessels; narrowing causes foraminal stenosis.
Intracranial granuloma
Intracranial granuloma (ICD-11 1D04.1) is a focal intracranial mass of macrophages and giant cells caused by infection (tuberculoma, fungal, parasitic), sarcoidosis, or foreign material; diagnosed by CT/MRI and biopsy.
Intracranial pressure
Intracranial pressure (ICP), also called intracranial hypertension when elevated, is the pressure inside the rigid skull from brain, blood, and CSF. Normal 7–15 mm Hg; above 20–25 mm Hg pathological, treated with osmotherapy, drainage, or craniectomy.
Intracranial space-occupying lesion
Intracranial space-occupying lesion (ICD-11 MB71.0, ICD-10-CM R90.0), also called intracranial mass lesion: any discrete intracranial lesion causing mass effect, mainly tumor, hemorrhage, abscess, or infarction, evaluated chiefly by contrast-enhanced MRI.
Intraocular medulloepithelioma
Intraocular medulloepithelioma, also called diktyoma, is a rare childhood embryonal tumor of the non-pigmented ciliary epithelium, the second most common pediatric intraocular tumor after retinoblastoma, linked to DICER1 mutations and treated mainly by enucleation.
Intraocular pressure
Intraocular pressure (IOP), also called eye tension, is the fluid pressure in the eye's anterior chamber, set by aqueous humor production and outflow; measured by tonometry, chiefly Goldmann applanation, and the main modifiable glaucoma risk factor.
Intrinsic primary afferent neuron of myenteric plexus
Intrinsic primary afferent neuron (IPAN), also called enteric primary afferent neuron or intrinsic sensory neuron: a sensory neuron with cell bodies in the myenteric and submucosal plexuses that transduces gut mechanical and chemical stimuli, has Dogiel type II morphology and AH electrophysiology, initiates local enteric reflexes, and does not project to the CNS.
Intrinsically photosensitive retinal ganglion cell
Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called melanopsin-expressing RGCs, are a third retinal photoreceptor class: about 1–2% of ganglion cells, six subtypes, mediating circadian entrainment, pupillary reflex, sleep, and mood.
Ioflupane (123I)
Ioflupane (123I), sold as DaTscan, is a radioactive cocaine analog that binds the dopamine transporter for SPECT imaging in parkinsonian syndromes and dementia with Lewy bodies.
Iris (anatomy)
Iris (anatomy): the colored diaphragm of the eye surrounding the pupil. Its sphincter and dilator muscles adjust pupil size to control light entry; melanin determines eye color, and its pattern is unique like a fingerprint.
Ischaemic optic neuropathy
Ischaemic optic neuropathy (ION, ischemic optic neuropathy): sudden painless vision loss from optic nerve infarction. Anterior (AION) and posterior (PION) forms; nonarteritic AION is the leading acute optic neuropathy over age 50, with no proven treatment.