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Smiths - Neuropsychology Glossary
Category: Health and Medicine > Neuropsychology Glossary
Date & country: 14/10/2007, UK
Words: 213

`Reduction in speech, movement, thought, and emotional reaction; a common result of bilateral frontal lobe disease` (Medical Search Engine, 2004).

Access Dysphasia
A type of dysphasia described by Warrington and McCarthy (1987) and characterised by difficulty retrieving semantic information from memory rather than by the loss of the underlying memory traces in any absolute sense. A difficulty in indexing that which is still there.

Acquired Dyscalculia
A dyscalculia arising in a previously skilled (and thus usually adult) subject, as a result of brain injury or disease.

Acquired Dyslexia
A dyslexia arising in a previously skilled (and thus usually adult) reader, as a result of brain injury or disease. The study of acquired dyslexia goes back to the age of the diagram makers, and clinical case studies have identified a number of subtypes, notably deep dyslexia and surface dyslexia. Modern interest in this topic was sparked by Marshall and Newcombe (1966, 1973). The essence of both classical and modern explanations is that normal reading ability reflects the coordinated simultaneous functioning of a number of discrete cognitive processes

Acute Disorder
A disorder posing an immediate threat. E.g. acute appendicitis. [Compare chronic disorder.]

Aggressive Disorder
A disorder of rapid onset or progression. Some progressive disorders can be more aggressive than others.

Strictly speaking, a total failure of gnosis. A state of not knowing what something is, or is for, in a confrontational naming task. [See now finger agnosia.]

Defective syntax in speech (but not, curiously enough, in automatic speech). A frequent sign of Broca's aphasia. [There is a longer discussion of agrammatism in Section 6.5 of our e-paper on `Speech Errors, Speech Production Models, and Speech Pathology`.]

Strictly speaking, a total inability to read the written word but with preserved visual perception of objects and pictures.

Alzheimer's Disease
[See firstly dementia; also known as dementia of Alzheimer's type (DAT).] Alzheimer's disease results from a remorselessly progressive loss of neural tissue at a microscopic level. Neurons are gradually replaced by non-excitable `plaques and tangles` until eventually what first shows itself clinically as mild forgetfulness advances into a total breakdown of all cognitive functions.

The general term for a defect of long-term memory, be it neurogenic or psychogenic in origin. Neuropsychology deals mainly with the amnesic syndrome and frontal amnesia.

Amnesic Syndrome
An amnesic state arising from a variety of causes, and characterised by a severe-to-total anterograde amnesia, accompanied by some degree of retrograde amnesia and a package of non-amnesic symptoms and signs such as attention deficits, irritability, and general emotional lability. Short-term memory, curiously enough, is intact up to 30 seconds or so, and general intelligence remains at the premorbid level. The syndrome is correlated anatomically with bilateral lesions of either the hippocampal regions or the mammillary bodies.

Strictly speaking, a total inability to carry out a skilled muscle movement, or, in the context of communication, a total inability to produce speech.

A congenital weakness in an artery wall, and therefore a likely point of eventual rupture and haemorrhage. Where the artery concerned is a cerebral artery, this is a predisposing factor to a haemorrhagic CVA.

Angular Gyrus
Gyrus at the junction of the parietal, temporal, and occipital lobes, and therefore admirably placed to support simultaneous interpretation of (respectively) somaesthetic, auditory, and visual information. [See Brodmann's Area 39 on Kleist's (1934) cortical localisation map. See also Gerstmann's syndrome.]

(1) A clinical sign readily discovered using a confrontational naming task. A naming disability very common in all the aphasias, and one of the key factors in the aphasic's reduced communicative success. A difficulty in retrieving words from the lexicon (1), although it is unclear whether this is due to damage to the lexicon itself, or to defective access to it. Nine different subtypes of anomia were identified by Benson (1979), including category-specific anomia, modality-specific anomia, semantic anomia, word production anomia, and word selection anomia. (2) A clinical syndrome. A type of aphasia (anomic aphasia) wherein anomia (1) is the predominant presenting sign.

Anomic Aphasia
See anomia (2).

Anterior Cingulate Gyrus
This is the proportion of the cingulate gyrus which is located anterior to the corpus callosum, that is to say, at Brodmann's Area #24 on the medial aspect of the Kleist (1934) brain map

Anterograde Amnesia
An amnesia which acts forwards in time from the moment of insult, and which is therefore characterised by a difficulty in consolidating new experience, that is to say, patients can have experiences, but they cannot recall them more than a few seconds after the event. They can therefore quite cheerfully have the same experiences over and over again without realising it.

Generic term for a wide variety of acquired neurogenic language disorders. An impairment to a greater or lesser extent of higher cognitive language processing, rather than of the more peripheral sensory and motor systems. Alternatively, `a multimodality reduction in capacity to decode (interpret) and encode (formulate) meaningful linguistic elements` (Darley, Aronson, and Brown, 1975, pp1-2). In Wernicke's aphasia, for example, words are poorly understood, despite an intact auditory system. Aphasias are conventionally divided into fluent and non-fluent types, and then into specific subtype syndromes.

Strictly speaking, a total inability to initiate voluntary motor movements, despite intact motor pathways.

Asperger's Disorder - Syndrome
See this entry in the companion glossary on `Self and Consciousness`.

An inability to coordinate skeletal muscular activity, leading to unsteadiness and defects of balance.

Ataxic Dysarthria
One of the six clinically distinct subtypes of dysarthria recognised by Darley, Aronson, and Brown (1975). [There is a longer discussion of the subtypes of dysarthria in Section 6.8 of our e-paper on `Speech Errors, Speech Production Models, and Speech Pathology`.]

[Greek = `without fixed position`] Term coined by Hammond (1871) to describe a state of continual motion (of hand, limb, etc.), often slow and writhing.

This from Baron-Cohen (1989): `Autism is a pervasive developmental disorder which begins in the first 36 months of life []. Symptoms include deficits in the pragmatic [Psycholinguistics Glossary] aspects of language [], an absence of symbolic play [], and the presence of ritualistic behaviour []. Autistic children also suffer a severe impairment in their ability to relate socially.` Autism has been a popular area of study of late, because the aforementioned pragmatic deficits generated a popular cognitive deficit explanation. As formulated initially by Baron-Cohen, Leslie, and Frith (1985), this explanation asserts that all the categories of autistic symptom can be traced back ultimately to a specific underlying disorder of second order representation, also referred to as an inability to form a theory of mind, or as mindblindness. As a result, autism studies are of as much interest to philosophers, psycholinguists, and neurobiologists, as they are to paediatric clinicians.

Hypothetically, auto-association is one of the basic properties of biological cell assemblies or computerised neural networks. The process detects the stable patterns in incoming stimulation, and creates an inter-associated set of neurons particular to each `constant form` within that stimulation. The resulting `learned` network is stable, exhibits part-to-whole retrieval, and can be further developed by experience. The concept is invoked in the distributed memory theory of Allport (1985), and provides a potential micro-mechanism for the entire psychological phenomenon of abstraction.

Automatic Speech
Over-learned and familiar phrases such as cursing, counting, reciting, and rhyme. Can be retained in Broca's aphasia and dementia even when non-automatic speech is affected. Presumably initiated, therefore, in an area other than Broca's Area, and possibly stored in the lexicon as single units despite being made up from individual words stored individually! [For an example, see McCarthy and Warrington (1984).]

[Greek ballein = `to throw`] A clinical sign. Uncontrolled flailing movements of arms or legs.

Of tumours, one which is not cancerous. [Compare malignant.]

The term describing any residual visual abilities following damage to either the geniculo-striate pathway and-or cortical area 17. Such residual abilities are fairly rudimentary aspects of vision such as the automatic shifting of gaze towards a light, and their effects are typically unconscious. [Further details and demonstration.]

Boston School
Doctrine of aphasiology which insists on mapping aphasic symptoms closely onto brain areas. [Compare globalist school.]

Bovine Spongiform Encephalopathy (BSE)
An untreatable progressive encephalopathy of cattle, characterised by a fairly aggressive deterioration of brain tissue, and probably due to the action of a prion, an abnormal protein. Also possibly transferrable to humans as Creutzfeld-Jacob disease.

Broca's Aphasia
A non-fluent aphasia characterised by effortful and halting speech, reduced phrase length, prosodic disturbance, and awkward articulation. Frequently shows dyspraxia of speech, long voice onset times, agrammatism, anomia (1), paraphasia, telegraphic speech, intrusive vowels, hesitations, consonant substitutions, repetition difficulties, and writing difficulties. Auditory comprehension is relatively intact (unlike Wernicke's aphasia), as is the willingness to engage in spontaneous interaction (unlike transcortical motor aphasia). Automatic speech is commonly spared. [See also Lichtheim's house.]

Broca's Area
The third frontal convolution of the left hemisphere, and the site of a classic Broca's aphasia. The area where Broca's patient, Leborgne, had his lesion. Consists of Brodmann's Areas 44 and 45 [to see where these are on the cortical map, click here].

See bovine spongiform encephalopathy.

Bulbar Palsy
Facial and/or pharyngeal palsy resulting from damage to medullary lower motor neurons. [Compare pseudobulbar palsy.]

An abnormal and uncontrolled process of cell division leading to the formation of a life-threatening growth. Can be sub-typed into carcinomas and sarcomas. Characterised by being able (a) to invade and destroy surrounding healthy tissue, and (b) to create metastases.

A cancer of epithelial tissue. [Compare sarcoma.]

Category-Specific Anomia
One of the nine clinically distinct subtypes of anomia (1) recognised by Benson (1979). A category-specific impairment in which there is a naming defect for some classes of objects but not for others. Such impairments might be for colours or uses, or for fruit and vegetables, or personal names, and are generally held to indicate some sort of categorical zoning of the lexicon (1).

Category-Specific Impairment
A class of cognitive impairment where the severity of the defect (a) depends in large part upon the semantic or grammatical nature of the test item, and (b) is common to other test items from the same semantic or grammatical category. Often presents as a selective anomia or agnosia, and is commonly taken as reflecting the underlying organisation of the lexicon. For a brief review of the history of this type of defect, see Warrington and Shallice (1984), and for a useful explanatory diagram, see Allport 1985.

Cell Assembly
A collection of interconnected-by-experience neurons capable of functioning as a physiological memory of that experience. [For a fuller definition and useful onward links, see our Main Glossary (C).]

Cerebro-Vascular Accident (CVA)
Brain damage arising from an acute episode of cerebro-vascular disease, with associated physical and psychological symptoms. `A syndrome characterised by rapidly developing clinical symptoms and/or signs of focal loss of cerebral function, in which symptoms last more than 24 hours [compare transient ischaemic attack]or lead to death, with no apparent cause other than that it is of vascular origin` (Rudd and Wolfe, 2002/2004 online). Occurs in two basic forms, namely the thrombotic form, resulting from a blood vessel blockage (perhaps as a result of an embolism or thrombosis), and the haemorrhagic form, resulting from a blood vessel bleed (perhaps as a result of an aneurism) [see Rudd and Wolfe, op. cit., for a more detailed classification]. Given the nature of the brain's blood supply, an infarct at one point will cause cell death [necrosis] at any point `upstream` which does not have an alternative blood supply, and given the nature of cellular chemistry that necrosis can itself cause diaschisis.

Cerebro-Vascular Disease
Deterioration of the brain's circulatory system, typically as the result of a progressive disorder. A common precursor to a cerebro-vascular accident.

See closed head injury.

[Greek choreia = `dance`] Poorly controlled skeletal movements, giving rise to irregular and involuntary lurching while walking, as well as intermittent grimacing.

Chronic Disorder
A permanent or long-standing disorder which poses no immediate threat. E.g. chronic bronchitis. [Compare acute disorder.]

Finding another way to say something when the word you really wanted to say is unavailable to the speech production process as a result of anomia (1).

Closed Head Injury (CHI)
A class of traumatic head injury. A `blunt instrument` bang on the head, such as occurs in boxing, some road traffic accidents, and many household or day-to-day blows to the head. Damages brain tissue indirectly, that is to say, by shaking it about. [See also concussion, and compare penetrating head injury.]

A period of profound and prolonged unconsciousness following disease or injury.

The clinical manifestation of the diaschisis, oedema, and other sequelae of a traumatic head injury; a period of raised intracranial pressure due to same, which can itself threaten to do yet further damage.

Conduction Aphasia
A fluent aphasia characterised by an impairment in verbal repetition far out of proportion to any fluency or comprehension deficits. The syndrome was predicted by Wernicke (1874) and confirmed by Lichtheim (1885). So named because although the verbal repetition task involves both comprehension and production processes at the same time, only the communication link between the two seems to be at fault. Symptoms include paraphasias and anomia (1) in a context of fluent melodic speech. Voice onset time, grammar, and comprehension are not impaired. Conduction aphasias are commonly attributed to lesions of the white matter arcuate fasciculus connecting Broca's area and Wernicke's area. [See also Lichtheim's house.]

[See firstly frontal lobe syndrome and dysexecutive syndrome.] An attempt to explain present evidence to a present audience but without a true recollection to go on [compare false recollection]. If the confabulation is in any way grandiose or unreasonable then it is termed fantastic confabulation, but if it is reasonable-but-just-inaccurate it is termed momentary confabulation (McCarthy and Warrington, 1990). [There is a longer discussion of confabulation in Section 9 of our e-paper on `From Frontal Lobe Syndrome to Dysexecutive Syndrome`.]

Confrontational Naming Task
A clinical assessment test requiring the patient to name objects by sight, sound, or touch, pictures by sight, and general sounds, tastes, and smells as appropriate. By its nature, a good screening test for anomia (1). [See also cueing.]

The philosophical doctrine that cognition can be modelled (and therefore better understood) by connecting up artificial neurons, either in fact, or in simulation on a computer, and the practical science thereof. [For a longer introduction to this topic, see our e-paper on `Connectionism`.]

One who practices connectionism.

Creutzfeld-Jakob Disease (CJD)
A progressive encephalopathy of humans, possibly a variant of bovine spongiform encephalopathy.

Crossed Aphasia
A right hemisphere aphasia. Occurs in 1-2% of all aphasias, and characterised by confusion, memory and attention defects, and personality change (in addition to the usual language deficits). Agrammatism is common, but comprehension and naming tend to be preserved.

A way of helping patients if they are having difficulty with a confrontational naming task. Cueing involves prompting them in some way, and the relative efficacy of different types of cues often reflects upon the organisation of the normal naming process. [See now first letter cueing, phonemic cueing, semantic cueing, and silent articulatory cueing.]

See cerebro-vascular accident.

Deep Dyslexia
A subtype of acquired dyslexia characterised primarily by difficulties at the word meaning level when reading aloud [compare surface dyslexia]. Typical problems include (a) semantic paralexical confusions (e.g. reading `stamps` for `postage`), (b) relative difficulty with abstract nouns compared to concrete nouns, and (c) poor reading of unfamiliar words or non-words. Coltheart (1980) explains the paralexias by arguing that one of the right hemisphere's main jobs is to establish the `superordinate semantic category` to which a printed word belongs. When a normal brain reads out loud, each stimulus word propagates firstly from the visual cortex to Wernicke's area, and then from Wernicke's Area to Broca's area. At the same time, it propagates into the right hemisphere to activate the appropriate categorial nodes in the broader semantic network. For the stimulus word STONE, this might be the node for [minerals

Déja Vu
[French = `already seen`] An inappropriate perceptual quale (plural = qualia). The erroneous belief that you have seen something or been somewhere before, when factually you have not. This is a truly puzzling symptom because it challenges the most fundamental definitions of an intact memory. William James, for example, defined memory as being accompanied by `the additional consciousness that we have thought or experienced it before` (James, 1890, p648; italics original). In cases of déja vu, however, this additional consciousness exists when logically it should not.

[Literally, to lose one's mind.] A generic term for a number of progressive medical conditions, all characterised by a gradual loss of perceptual, memory, and higher cognitive functions. The best known dementia is Alzheimer's disease, but see also multiple-infarct dementia and compare senile dementia.

Developmental Dyslexia
[See firstly NB1 above.] A dyslexia arising in someone learning to read (and thus usually pre-adult), possibly as a result of brain injury or disease. The study of developmental dyslexia goes back to the late 19th century, when Pringle-Morgan (1896) reported it in the case of Percy, a 14-year-old boy. Modern interest in this topic was sparked by the sustained controversy over recent decades over poor national literacy levels, and the failure of a parade of educational initiatives to improve matters. [There is a longer introduction to this subject in our e-paper on `Dyslexia and the Cognitive Science of Reading and Writing`.]

Developmental Verbal Dyspraxia
[See firstly NB1 above.] The developmental form of dyspraxia of speech.

Diagram Makers
School of nineteenth century aphasiologists who argued strongly for the precise localisation of language functions. Typically Wernicke (1874) and Lichtheim (1885). Lichtheim's house is a good example of the diagrams drawn by the diagram makers.

Neural shock, that is to say, the temporary suppression of response in healthy neural tissue close to the site of an actual lesion. Typically, this will be due to swelling at, or chemical contamination from, the primary site. Either way, it results in behavioural deficits greater than would otherwise be expected, but in respect of which some degree of spontaneous recovery may confidently be expected.

Disconnection Syndrome
A neurogenic disorder (of language or whatever) caused by subcortical (white matter) damage rather than by cortical (grey matter) damage. This means that the separate modules of a distributed (i.e. `modular`) processing system can remain physically intact within themselves, but lose their ability to interact meaningfully with each other, thus degrading the overall performance of the system in question. Conduction aphasia is a typical disconnection syndrome. [Crosson (1985) gives some idea of the potential complexity of the subcortical pathways linking related cortical areas, if interested.]

`A disorder with a specific cause and recognisable signs and symptoms; any bodily abnormality or failure to function properly, except that resulting directly from physical injury` (Oxford Dictionary for Nurses).

See the more detailed coverage of this topic in the companion Mental Philosophy Glossary.

Dissociation (of Function)
The selective loss of a particular cognitive ability following a localised brain injury, so named because the failing ability `dissociates`- that is to say, moves away - from the remaining intact abilities. One of the classic examples of a dissociation is the disproportionate damage to the fluency of language production produced by lesions in Broca's Area. [See now double dissociation.]

Double Dissociation
[See firstly dissociation.] Term coined by Bagshaw and Pribram (1965) and popularised by Warrington and Rabin (1970) to refer to two in-some-way complementary dissociations. The classic example of a double dissociation is that between the sentence production deficits found with lesions in Broca's Area and the sentence comprehension deficits subsequently found with lesions in Wernicke's Area. The complementarity derives from the fact that the earlier discovery in some way directly invited the search for the second.

Strictly speaking, a less than total impairment of the ability to move a muscle group despite an otherwise adequate intention, or - in the context of communication - an impaired inability to produce speech. In this latter respect, `a group of speech disorders resulting from disturbances in muscular control` (Darley, Aronson, and Brown, 1975, pp1-2). [Compare anarthria.] [See separately ataxic dysarthria, flaccid dysarthria, hyperkinetic dysarthria, hypokinetic dysarthria, mixed dysarthria, and spastic dysarthria.]

Strictly speaking, a less than total defect of number processing, with both acquired and developmental forms. [There is a longer discussion of the brain's involvement in numeracy in our e-paper on `The Psychology of Numeracy`.]

Strictly speaking, a less than total defect of written language processing, most conveniently dealt with under two major subtypes, namely acquired dyslexia and developmental dyslexia.

Avoid - use anomia instead.

Strictly speaking, a less than total aphasia, but in practice a simple synonym for aphasia. [See NB2 above.]

Strictly speaking, a less than total defect of praxis, common as a result of CVA or other pathology. An `inability to act or to move various parts of the body in a purposeful manner, although the power of movement is intact. There is no paralysis and the patient understands what is required of him; yet he cannot execute the action he wishes to perform` (Head, 1926, p94). In children, often known as clumsy child syndrome or minimal brain dysfunction.

Dyspraxia of Speech
A subset of the dyspraxias, presenting as a specific difficulty in initiating vocalisation, accompanied by effortful production and defective prosodic quality. A disorder of `brain circuits devoted specifically to the programming of articulatory movements` (Darley, Aronson, and Brown, 1975, pp1-2). General intellectual level is not necessarily impaired. In children, often known as developmental verbal dyspraxia. [There is a longer discussion of dyspraxia of speech in Section 6.7 of our e-paper on `Speech Errors, Speech Production Models, and Speech Pathology`.]

A clinical sign. The automatic repetition of all that the patient hears. Frequently found in transcortical motor aphasia and Tourette's Syndrome.

A clinical sign. The automatic mimicking of the physical movements of others. Frequently found in Tourette's Syndrome.

A clot or other floating obstruction in a blood vessel. Can cause a thrombotic CVA.

A viral or bacterial infection of the brain or brainstem, resulting in inflammation and cell death.

Cell death degeneration of the brain or brainstem.

The doctrine that psychological consciousness is an incidental by-product (i.e. epi-phenomenon) of neural activity, but has no causal influence upon it.

False Recollection
A false memory. An act of apparent recall; one which is perceived as genuinely having happened, but which does not, in fact, reference a real occurrence. [Compare confabulation.]

Finger Agnosia
[See firstly agnosia.] Finger agnosia is a mental confusion over the location of your fingers in space, by sight, and/or across the left-right divide. For its role in Gerstmann's Syndrome, see the companion resource `The Psychology of Numeracy`, and for how it can be detected, see `A Gentle Introduction to Finger Agnosia`.

First Letter Cueing
A type of cueing. Involves giving the initial letter of the target word in the hope that this will help the patient access the lost speech output patterns (e.g. `It begins with a K [pronounced `kay`] .....`). Make sure you say the letter name, and not the phonetic sound of the letter. [Compare phonemic cueing, semantic cueing and silent articulatory cueing.]

First Order Representation
See representation, first order.

Flaccid Dysarthria
One of the six clinically distinct subtypes of dysarthria recognised by Darley, Aronson, and Brown (1975). [There is a longer discussion of the subtypes of dysarthria in Section 6.8 of our e-paper on `Speech Errors, Speech Production Models, and Speech Pathology`.]

Fluent Aphasia
An aphasia with generally retained word production ability (although nonetheless frequently paraphasic or jargonaphasic). Three types of aphasia are usually classed as fluent, namely Wernicke's aphasia, conduction aphasia, and transcortical sensory aphasia. [Compare non-fluent aphasia.]

Frontal Amnesia
An amnesic state associated with damage to the frontal lobes, and characterised by confabulations and difficulties with problem solving tasks requiring forward planning. [There is a longer discussion of the memory correlates of frontal lobe injury in our e-paper on `From Frontal Lobe Syndrome to Dysexecutive Syndrome`.]

The term `fugue` has long been applied to transient amnesic states in which there is loss of access to either the semantic or episodic aspects of the self, and which commonly results in the sufferer wandering aimlessly away from their normal workplace or home. This clinical pattern of signs was elevated by the DSM-IV into `dissociative fugue`, one of the four specific dissociative disorders, describing it as follows .....

Functionalism (1)
The classical philosophical doctrine that the mind's mental operations exist (and implicitly do not come cheaply in the first place) for their practical value in satisfying the needs of a vulnerable organism in an hostile environment. Arose around the turn of the 19th/20th centuries from the writings of John Dewey and James Angell at the University of Chicago. [Full history]

Functionalism (2)
Modern form of functionalism (1). The philosophical doctrine that there is value to be had from analysing cognitive processes in isolation, i.e. separated from considerations of brain anatomy. Borrows heavily from computer science (hence cannot predate the computer era). Arose during the 1950s from early theories of attention and memory, and now typified by the various competing logogen theories. Clearly seen in the writings of David Marr, and especially in his notion of the computational level of cognition (Marr, 1982). [Full discussion. For a nice introduction to Marr's work, see McClamrock (1991/2004 online).]

Gerstmann's Syndrome
Gerstmann (1930) described an acquired neurogenic syndrome in which four distinct signs tended to co-occur. These were (a) `finger agnosia`, an inability to tell one finger from another, (b) right-left disorientation, (c) writing difficulties, and (d) dyscalculia. This syndrome seemed to follow damage centred on the angular gyrus of the dominant hemisphere.

Global Aphasia
A severe-to-total impairment of all communicative (if not all cognitive) ability. Common just after a CVA or THI, but frequently relieved by spontaneous recovery. Best described by the everyday phrase `the lights are on but there's nobody in`!

Globalist School
Those aphasiologists - including Jackson, Freud, and many others - who believe(d) that the brain works as a holistic system, and who therefore caution(ed) against trying to attribute specific functions to specific areas. [Compare diagram makers and Boston school.]

The word `gnosis` means knowing something for what it is, recognising it, evaluating its significance, knowing what it does and - perhaps more importantly - what you should do about it. States of gnosis are the logical end-result of the broader process of perception, and are by that token quite vulnerable to brain damage. If impaired, the resulting condition is known as an agnosia.

Herpes Simplex Encephalitis (HSE)
An infection of the brain by the herpes simplex virus.