1,240 articles
Laser Corneal Surgery
Laser corneal surgery (LASIK, PRK/TransPRK, SMILE) reshapes the cornea with excimer or femtosecond lasers to correct myopia, hyperopia, and astigmatism; evidence shows comparable efficacy and predictability across modern techniques.
LASIK
LASIK (Laser-Assisted In Situ Keratomileusis) is eye surgery in which a hinged corneal flap is folded back and an excimer laser reshapes the cornea to treat refractive errors.
Lateral geniculate nucleus
Lateral geniculate nucleus (LGN), also lateral geniculate body: thalamic relay nucleus of the visual pathway, with six magnocellular, parvocellular, and koniocellular layers, sending optic radiations to primary visual cortex.
Lateral grey column
Lateral grey column (lateral horn, columna grisea lateralis medullae spinalis): small lateral projection of spinal cord grey matter at T1–L2/L3 containing preganglionic sympathetic neurons (intermediolateral cell column), with axons reaching the sympathetic trunk via white rami communicantes.
Laterality
Laterality: the scientific study of left-right asymmetries in brain, behavior, and cognition, from human handedness and language dominance to animal lateralization; also the name of the interdisciplinary journal founded in 1996 by Bryden, Corballis, and McManus.
Lateralization of brain function
Lateralization of brain function: task-specific hemispheric biases, with left-hemisphere language dominance in about 95% of right-handers and right-hemisphere spatial and face-processing advantages, distinct from the debunked left-brained versus right-brained personality myth.
Lattice corneal dystrophy type I
Lattice corneal dystrophy type I (LCD1, Biber-Haab-Dimmer, classic lattice corneal dystrophy) is a rare autosomal dominant TGFBI (5q31, R124C) amyloid stromal corneal dystrophy causing lattice lines, erosions, and vision loss from the first decade, treated with PTK or keratoplasty.
Lazarus sign
Lazarus sign: complex spinally mediated arm-flexion movement in brain-dead patients, named by Ropper 1984, occurring in about 2% during apnea testing or ventilator withdrawal; does not invalidate brain-death diagnosis.
Leptomeningeal carcinomatosis
Leptomeningeal carcinomatosis, also called leptomeningeal metastasis or neoplastic meningitis, is spread of cancer cells within the leptomeninges and subarachnoid space, affecting about 5% of cancer patients, most often from breast, lung cancer, or melanoma, diagnosed by CSF cytology and MRI.
Lesion of common peroneal nerve
Lesion of common peroneal nerve (peroneal nerve palsy, common fibular nerve dysfunction, ICD-10 G57.3): injury to the sciatic-nerve branch at the fibular neck causing foot drop, eversion weakness, and sensory loss; graded by Sunderland classification.
Lesion of plantar nerve
Lesion of plantar nerve (ICD-11 8C11.6): damage to the medial or lateral plantar nerves, tibial nerve branches below the tarsal tunnel. Causes include entrapment, trauma, and surgery; presents with burning pain, paresthesias, jogger's foot, Morton's neuroma.
Lesion of radial nerve
Lesion of radial nerve (ICD-10 G56.3, ICD-11 8C10.2), also called radial neuropathy or radial nerve palsy: injury to the radial nerve causing wrist drop, most often from humeral fracture or compression, usually recovering with splinting.
Lesion of ulnar nerve
Lesion of ulnar nerve (ICD-11 8C10.1): ulnar neuropathy, usually cubital tunnel syndrome at the elbow or Guyon canal syndrome at the wrist; second most common upper-limb entrapment neuropathy, treated conservatively or surgically.
Levobunolol
Levobunolol (levobunolol hydrochloride ophthalmic solution) is a noncardioselective topical beta-blocker, distinct from timolol and betaxolol, used once or twice daily to lower intraocular pressure in open-angle glaucoma and ocular hypertension.
Lewy body
Lewy body: intraneuronal aggregate of misfolded alpha-synuclein protein, discovered by Friedrich Lewy in 1912. Defines Parkinson's disease, dementia with Lewy bodies, and Parkinson disease dementia; definitive diagnosis requires autopsy.
Lie detection
Lie detection, best known through the polygraph or lie detector, infers deception from physiological responses. Invented by Marston, Larson, and Keeler in the 1910s-1920s, it is above chance but scientifically weak, excluded from most courts, and used mainly for security screening.
Lightheadedness
Lightheadedness, also called light-headedness or presyncopal dizziness, is a vague faint or floating sensation, one of four dizziness types, caused by reduced cerebral blood flow (orthostatic hypotension, arrhythmia), hyperventilation, anxiety, or medications.
Limbic system
Limbic system: forebrain structures common to all mammals (amygdala, hippocampus, hypothalamus, cingulate gyrus, septal nuclei, anterior thalamus) implicated in emotion, memory, and survival behaviors; term coined by MacLean in 1952 from Broca's 1878 limbic lobe and Papez's 1937 circuit.
Lingual papillae
Lingual papillae (papillae linguales) are mucosal projections on the tongue's dorsal surface, of four types: filiform, fungiform, foliate, and circumvallate; only filiform lack taste buds, and fungiform are ectoderm-derived while circumvallate and foliate are endoderm-derived.
Lissencephaly
Lissencephaly (smooth brain), including agyria, pachygyria, and subcortical band heterotopia, is a cortical malformation from defective neuronal migration at 12-24 weeks gestation, mainly caused by PAFAH1B1 (LIS1) and DCX mutations, with epilepsy and short life expectancy.
List of animals by number of neurons
List of animals by number of neurons: ranked neuron counts, from fruit fly (166,000) and octopus (500 million) to human (86 billion) and African elephant (257 billion), with counting methods and limits as intelligence predictors.
List of nerves of the human body
List of nerves of the human body: the 12 pairs of cranial nerves (olfactory through hypoglossal) and 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal), plus major named peripheral nerves such as the sciatic, median, and vagus.
List of neurological conditions and disorders
Neurological conditions and disorders, also called nervous system diseases, affect the brain, spinal cord, and nerves; over 600 exist, including stroke, epilepsy, migraine, Alzheimer's, Parkinson's, and multiple sclerosis, the leading global cause of disability.
List of Nobel laureates in Physiology or Medicine
List of Nobel laureates in Physiology or Medicine: annual prize awarded 116 times to 232 laureates 1901-2025, first to Emil von Behring; selected by the Nobel Assembly at Karolinska Institutet; 2026 went to Deisseroth, Hegemann, and Nagel for optogenetics.
List of regions in the human brain
Regions of the human brain: cerebrum, cerebellum, brainstem (midbrain, pons, medulla), diencephalon, six cerebral lobes, cortical areas, and modern atlas parcellations such as AHRAv2 and Brodmann areas.
Lobes of the brain
Lobes of the brain: the six conventional divisions of each cerebral hemisphere (frontal, parietal, temporal, occipital, insula, limbic), their sulcal and imaginary-line boundaries, lobe-level functions, and the history and limits of functional localization.
Local anesthesia
Local anesthesia: numbing a limited body area with sodium-channel-blocking drugs while the patient stays conscious. From cocaine (Koller, 1884) and Bier's 1898 spinal to lidocaine, bupivacaine, LAST management, and local-versus-general outcome comparisons.
Local Field Potential Measurement
Local field potential (LFP) measurement records low-frequency extracellular brain voltage, below about 300 Hz, from intracerebral microelectrodes; also called micro- or depth EEG. It reflects summed synaptic currents of neuronal populations and is used in adaptive deep brain stimulation.
Local interneuron
Local interneuron (local circuit neuron): a neuron with a locally confined axon; in cortex, GABAergic cells (~20-30% of neurons) in PV, SST, and 5HT3aR classes, born in ganglionic eminences, linked to epilepsy, schizophrenia, autism.
Locked-in syndrome
Locked-in syndrome (LIS): rare neurological state of quadriplegia, anarthria, and lower cranial nerve paralysis with fully preserved consciousness, usually from ventral pons stroke; communication via eye movements, eye trackers, or BCIs.