The Nervous System · Part Two · How It Senses and Moves
Lesson 30 / 61
The Brainstem: Architecture, Reticular Core, and Localization
The narrow bridge where the whole brain meets the whole body.
The brainstem is the stalk of midbrain, pons, and medulla that carries every ascending and descending pathway and houses the nuclei for cranial nerves III through XII. Its reticular core holds arousal, posture, breathing, and blood pressure, and it reaches the cord, the thalamus, the hypothalamus, and the basal forebrain from the same few centimeters of tissue. The Unified Model of Tone puts arousal, postural gain, autonomic outflow, and gaze at one address in this core, which is why an input here reaches outputs it never touched.
Pressor source
Rostral ventrolateral medulla
Vestibular nuclei
Four major, three minor, at the pontomedullary junction
Internal laminae
Tectum, tegmentum, basis
Breathing rhythm generator
Pre-Bötzinger complex, ventrolateral medulla
The brainstem
The brainstem runs from the caudal edge of the diencephalon down to the first cervical segment of the cord, with the fourth ventricle opening across its back at the pons and upper medulla. Cranial nerve nuclei sit in the tegmentum on the floor of that ventricle, and the long descending motor pathway runs in front of them through the basis. Because those nuclei are ordered by function from the midline outward, a small paramedian lesion takes eye or tongue movement while a lateral lesion of the same size takes pain, temperature, and balance.
The reticular core
The net of cells running through the center of all three tiers, and the place this stalk holds its tone. Tone is the organization a nervous system is holding when the next signal arrives. What returns from a perturbation is decided by that organization, not by the size of the perturbation. This core is read three ways: as the gain set on a descending pathway, as the arousal state the cortex is held in, and as the pressure and the breathing rhythm the medulla defends.
01Three tiers, three laminae
The brainstem packs three tiers and three laminae into one column
The brainstem stacks three tiers from the diencephalon down to the cord: the midbrain, the pons, and the medulla oblongata. Each tier carries its own cranial nerve nuclei. The midbrain serves nerves III and IV, the pons serves V through VIII, and the medulla serves IX through XII. Brainstem infarcts account for nearly one third of all ischemic strokes. Medullary infarcts are about 7 percent of ischemic brainstem strokes, and pontine infarcts are the most common of them Gowda 2026.
A second geometry runs across the first. Three laminae extend the entire length of the stalk: the tectum behind, the tegmentum in the middle, and the basis in front Angeles Fernández-Gil 2010. The tegmentum holds the cranial nerve nuclei and the reticular formation. The basis carries the long descending motor tracts. Every signal climbing toward thought and every command descending toward muscle passes single file through this column.
Where a nucleus sits predicts what it does
The tegmental nuclei are ordered by function from the midline outward: somatic motor nearest the midline, then visceral motor, then visceral sensory, then somatic sensory Angeles Fernández-Gil 2010. All the ascending somatosensory tracts cross the tegmentum in front of that row of nuclei. The tectum behind them holds no cranial nuclei, no tracts, and no reticular formation, so the diagnostic territory of the stalk is the middle lamina and the one in front of it.
A lesion of a few millimeters can sever pathways that span the entire neuraxis. Brainstem strokes therefore present with crossed signs, an ipsilateral cranial nerve palsy paired with contralateral motor or sensory loss Gowda 2026. How variable those presentations are follows directly from how tightly the corticospinal tract, the cranial nerve nuclei, the transverse pontocerebellar fibers, and the reticular activating pathways are packed against one another.
02Findings
What the research shows
03The reticular core
The reticular formation sets the gain on everything the brainstem carries
A diffuse net of neurons runs through the central core of all three tiers and governs arousal, the sleep-wake cycle, and baseline muscle tone. Magoun's group showed the mechanism directly. Stimulating the reticular formation of the medulla, pons, and midbrain tegmentum in cats abolished synchronized discharge and replaced it with low-voltage fast activity, an effect carried by a thalamic projection system Wijdicks 2019. The cortex woke because the brainstem told it to.
Lesions of the ascending reticular activating system cause coma, the most severe disorder of consciousness Edlow 2012. High angular resolution diffusion imaging of three adult human brains traced the pathways running from the brainstem to the thalamus, the hypothalamus, and the basal forebrain. Each carries a different distribution of neurotransmitter-specific fiber tracts. Arousal leaves the core along several chemically distinct routes.
The pontomedullary reticular formation sets postural tone
Cholinergic projections from the pedunculopontine tegmentum, together with forebrain and cerebellar efferents, converge on the mesencephalic and pontomedullary reticular formation, which distributes postural muscle tone and locomotion through a functional topography Takakusaki 2016. That topography was mapped largely in decerebrate cat preparations. Cortex, cerebellum, and brainstem meet on the same cells. Reticulospinal fibers then run to the cord, where they suppress postural muscle tone and shape posture against gravity.
The cortical half of that convergence has been mapped in man. Tractography across 1,065 Human Connectome Project diffusion datasets traced the corticoreticular pathway through the anterior and posterior limbs of the internal capsule Boyne 2022. The fibers partially decussate in the midbrain tegmentum and converge bilaterally on the pontomedullary reticular formation. Their cortical origins overlap the corticospinal tract across most of motor cortex, with additional exclusive input from medial and anterior prefrontal cortex. Descending command reaches the body by two roads, and one of them ends in the reticular core instead of on a motor neuron.
The same reflex changes size with the job
Brief impulses delivered over C7 or the sternum in 11 human subjects evoked short-latency responses in soleus, at 57.5 ms to the C7 impulse and 66.4 ms to the sternal impulse. Tibialis anterior answered at 51.7 and 55.4 ms in the same order Teng 2017. The latency arithmetic ruled out the corticospinal tract. Triceps held the same tonic activity in two conditions and returned a response 23.0 percent above background EMG while the arm supported about 40 percent of body weight, against 3.3 percent during an isometric contraction. Soleus and tibialis anterior shifted the opposite way.
Head rotation changed the numbers again, with responses growing larger contralateral to the direction of rotation Teng 2017. Neck position reaches reticulospinal output inside the latency of the postural reflex itself. A reticular core in health changes what a pathway returns when the job changes, which is what the 23.0 percent against 3.3 percent difference in triceps measures. A core stuck at one gain hands back the same reflex to a stumble and to a quiet isometric hold, and the margin that difference buys is gone.
04Medullary survival centers
The medulla holds pressure, cortical perfusion, and breathing from nuclei millimeters apart
The medulla runs pressure, cortical perfusion, and breathing from nuclei that sit millimeters apart. The rostral ventrolateral medulla sets sympathetic tone to the heart and vessels, which makes it the principal pressor source of the brainstem. The same region regulates respiration, glycemia, vigilance, and inflammation, and its rostral end holds the retrotrapezoid nucleus, the main central respiratory chemoreceptor Guyenet 2022. The beat-to-beat arithmetic of the baroreflex belongs to autonomic regulation.
The medulla sets cortical blood flow and cortical rhythm
Electrical stimulation of the RVLM in anesthetized spinalized rats raised regional cerebral blood flow by 31 percent and cut cerebrovascular resistance by 26 percent Golanov 2000. It also synchronized the EEG, raising power in the 5 to 6 Hz band by 98 percent. The animals were spinalized, so the cortex was answering the medulla and not a systemic pressure change.
A lesion traced the route. Destroying the medullary cerebral vasodilator area in the same rats cut the flow response by more than 59 percent and the EEG response by 78 percent Golanov 2000. This pathway slows cortical rhythm while raising cortical perfusion, which is a different operation from the desynchronizing arousal the reticular activating system drives. Gain in this stalk is set on the cortex's supply as well as on its signal.
One input, three different answers
Infusing 1 mol/L NaCl into the cerebral ventricles of rats split 24 recorded spinally projecting RVLM neurons into three populations: 46 percent excited, 37 percent inhibited, and 17 percent unchanged Stocker 2015. Sympathetic outflow fractionated with them. Lumbar and adrenal nerve activity rose, splanchnic activity held steady, and renal activity fell. Microinjecting muscimol into the RVLM abolished the sympathoexcitatory response. Sympathetic drive leaves the medulla through a bank of separately addressed channels, and one chemical signal moves each of them differently.
Inhibition inside the RVLM is graded and timed. Microinjecting the glycine receptor antagonist strychnine into the RVLM of anesthetized rats cut the duration of baroreflex-mediated inhibition of renal sympathetic nerve activity from 12 minutes to 5.1 minutes Gao 2019. Under steady-state conditions glycine supplies under 25 percent of the inhibition reaching those cells, and when synaptic drive rises glycine climbs to 47 percent while GABA falls to 53 percent. The medulla changes which transmitter holds a cell down according to how hard that cell is being driven.
Breathing and swallowing neurons sit millimeters apart and degenerate separately
Serial sections of brainstems from 19 normal individuals located the human pre-Bötzinger complex in the ventrolateral medulla, built of loosely scattered, small, lipofuscin-rich neurons carrying neurokinin 1 receptor and somatostatin Schwarzacher 2011. In a separate series of 10 multiple system atrophy cases, which carry central respiratory deficits without swallowing trouble, those neurons were reduced while the pharyngeal motoneurons of the nucleus ambiguus were spared. In 8 spinocerebellar ataxia type 3 cases, which carry dysphagia without reported respiratory deficits, the pattern reversed.
The nucleus ambiguus resolves further under genetics. Single-cell RNA sequencing in mice found three molecularly distinct populations at one address, marked by Crhr2, Vipr2, and Adcyap1, and the Crhr2 cells proved to be the ones innervating the esophagus Coverdell 2022. Driving all of the nucleus suppressed heart rate. Driving the Crhr2 population alone left heart rate untouched.
Waking hides the lesion that sleep exposes
Ablating neurokinin 1 receptor neurons on one side of the rat pre-Bötzinger complex left resting waking breath stable while wrecking breathing in REM sleep. Central apneas and hypopneas rose to 36.8 episodes per hour of REM against 6 before injection McKay 2008. Descending drive buffers the medullary rhythm in waking and exposes it when that drive withdraws.
Chemical drive to the medulla has an address of its own. The retrotrapezoid nucleus of the rostral medulla senses protons and holds arterial PCO2 near constant across sleep and waking, with paracrine help from the astrocytes and blood vessels around it Guyenet 2019. The rhythm generators and their chemoreceptors are worked through on respiration and the viscera.
05Gaze and the vestibular floor
Eye movements localize a brainstem lesion to a tier and a side
Vertical and torsional eye movements are generated in the midbrain and horizontal movements in the pons Strupp 2014. The direction of an ocular deficit therefore names a brainstem tier before anything else does. Isolated vertical dysfunction points to the rostral interstitial nucleus of the medial longitudinal fasciculus, the interstitial nucleus of Cajal, and the posterior commissure. Isolated failure of horizontal saccades points to the paramedian pontine reticular formation.
Gaze-evoked nystagmus divides on the same lines. A purely vertical form localizes to the midbrain and a purely horizontal form to a pontomedullary lesion Strupp 2014.
Downbeat nystagmus points away from the stalk
Downbeat nystagmus is most often caused by a bilateral floccular lesion or floccular dysfunction, not by damage to the brainstem tiers Strupp 2021. Pierrot-Deseilligny's 2005 review found no reported clinical case of downbeat nystagmus from focal brainstem damage Pierrot-Deseilligny 2005. Downward vestibular signals travel in the medial longitudinal fasciculus alone, while upward signals use both the MLF and the ventral tegmental tract. Upbeat nystagmus does arise from focal brainstem lesions, at the pons or the caudal medulla. A vertical nystagmus therefore sorts the patient into the stalk or the flocculus before any scan is ordered.
A broken medial longitudinal fasciculus carries the ocular tilt reaction with it
Impaired adduction on the side of the lesion is the pathognomonic sign of a broken medial longitudinal fasciculus, and it carries the name internuclear ophthalmoplegia Strupp 2014. In 410 patients collected by one examiner over 33 years, infarction caused 157 cases at 38 percent, multiple sclerosis 139 at 34 percent, and unusual causes 114 at 28 percent Keane 2005. The sign was unilateral in 87 percent of infarct cases and 27 percent of multiple sclerosis cases, so laterality itself reports on cause.
The ocular tilt reaction travels with the same fasciculus. A series of 120 held 87 patients with unilateral internuclear ophthalmoplegia. Subjective visual vertical was tilted in 96 percent of them and ocular torsion appeared in 79 percent, while skew deviation reached only 50 percent Zwergal 2008. In the 33 bilateral cases only 9 percent showed any component, so a symmetrical break in roll-plane signaling leaves no imbalance to see. Distinct lesions appeared on MRI in 68 percent, and 96 percent of those projected onto the pontomesencephalic MLF. Sensitivity grades the triad: subjective visual vertical first, ocular torsion second, skew deviation last.
Recovery separated the two kinds of deficit. Subjective visual vertical and ocular torsion normalized faster than the adduction deficit Zwergal 2008. Central compensation absorbs a vestibular tone imbalance within days. Adduction returns only as the fasciculus itself recovers.
Torsion sorts peripheral from central at the pontomedullary junction
Torsional deviation sorts along a line at the pontomedullary junction Sheth 2022. Lesions caudal to it produce ipsiversive torsion, whether they sit in the labyrinth, the eighth nerve, or the vestibular nucleus. Lesions rostral to it produce contraversive torsion. Central torsion is conjugate, with incyclotorsion in the higher eye and excyclotorsion in the lower. Torsion from a peripheral ocular motor palsy is disconjugate.
The vestibular nuclei sit at that junction: four major nuclei (medial, descending, superior, lateral) with three smaller ones alongside them Barmack 2003. Second-order vestibular neurons pool inner-ear signals with optokinetic, central visual, and neck proprioceptive input, and they cannot distinguish which source drove them. They do distinguish active movement from passive movement, which is a judgment about what the body itself just ordered.
A drifting gaze or a tilted head names the tier of the stalk that has faltered, and it names it in seconds.
06Crossed syndromes
Crossed signs name the millimeter where a brainstem pathway went quiet
Brainstem lesions produce crossed syndromes: a cranial nerve deficit on one side paired with a long-tract deficit on the other. The stalk compresses motor, sensory, autonomic, and cranial nerve systems into one column Gowda 2026. That pairing lets a clinician name a tier and a side from the bedside examination alone.
One small lateral medullary infarct carries the argument. Among 33 consecutive patients with Wallenberg's syndrome, Horner's syndrome appeared in 91 percent, ipsilateral limb ataxia in 85 percent, and contralateral hypalgesia in 85 percent Sacco 1993. A descending sympathetic pathway, a cerebellar pathway, and the spinothalamic tract run within millimeters of one another. Head CT was abnormal only when a cerebellar infarction was present, so the bedside triad outperformed the scan.
The medial syndrome, and how often it is complete
Medial medullary infarction mirrors the lateral syndrome, pairing tongue weakness on the side of the lesion with hemiparesis on the other. Among 4,200 consecutive acute ischemic strokes, 11 were MRI-proven medial medullary infarcts Kumral 2002. Medial medullary infarction accounts for under 1 percent of vertebrobasilar strokes. Seven of the 11 showed classical Dejerine syndrome: contralateral hemiparesis, lemniscal sensory loss, and ipsilateral lingual palsy from cranial nerve XII. The remaining four presented as pure hemiparesis, sensorimotor stroke, or bilateral infarction. The crossed pattern localizes powerfully when it appears, and it appears in full about two thirds of the time.
Bedside signs beat early imaging
In 101 patients with acute vestibular syndrome, a three-step oculomotor examination was 100 percent sensitive and 96 percent specific for stroke Kattah 2009. Early diffusion-weighted MRI was falsely negative in 12 percent of cases, all within 48 hours of onset. Skew deviation appeared in 17 percent overall: 4 percent of peripheral cases, 4 percent of pure cerebellar cases, and 30 percent of cases with brainstem involvement. A pattern of eye signs found the lesion the scan had missed.
07Silent below 95 mm Hg
The brainstem's answer to a somatic input has a measured threshold
The brainstem answers a somatic input according to the pressure and rate it is already holding. Stimulating the inferior alveolar nerve in cats produced a trigeminal depressor response only when prestimulus mean arterial pressure exceeded 95 mm Hg and heart rate exceeded 140 beats per minute Ohshita 2004. Below those values the same stimulus produced no cardiovascular response. After spinalization or a lesion of the RVLM the response disappeared entirely, and the responsible RVLM neurons traced to the intermediolateral nucleus of the cord.
The Unified Model of Tone states the reading as its own. An input does not carry its effect with it. The effect is produced by the organization the input lands in, which is why one nerve stimulus is silent below 95 mm Hg and depressor above it. Correspondence, and not force, is what makes an input specific. The cats below threshold did not need a larger stimulus. They needed a different state.
Body-wall input moves what the medulla defends
Barosensitive neurons in the nucleus of the solitary tract are selectively inhibited while sympathoexcitatory neurons in the rostral ventrolateral medulla are excited, and the defended pressure moves with them. Potts proposed that route in a 2006 review of baroreflex resetting during exercise, built on evidence that GABAergic inhibition in the solitary nucleus changes rapidly and reversibly Potts 2006. A defended pressure is a setting the brainstem holds, and input from the body wall reaches that setting itself.
The neck is one of the inputs the brainstem computes with
Second-order vestibular neurons at the pontomedullary junction receive neck proprioceptive input alongside inner-ear and visual input, and they cannot tell which source drove them Barmack 2003. Human reticulospinal postural responses changed size with head rotation inside the latency of the reflex itself Teng 2017.
Nowhere else is so much regulation packed into so little tissue, so an input to the neck is never a local event. Chiropractic care delivers graded mechanical input to the joints and muscles of the neck, and those afferents are among the ones these second-order cells pool. The Unified Model of Tone reads what follows from that convergence. A neck input reaches the cells that hold gaze and the reticulospinal cells that set postural gain in the same instant, so its effect shows up at outputs the contact never touched. How large that effect is depends on where the medulla has its pressure set, which the cats put at 95 mm Hg.
One organization sits in the reticular core, and every reading in this lesson is a reading of it. Three of them are taken here. The size of the reflex that core returns to the same muscle under two different jobs. The pressure the medulla defends against a somatic stimulus. The breathing rhythm that core buffers in waking and abandons in REM sleep. The research page on the autonomic nervous system takes up what each of those measures reports.
The brainstem turns a scattering of small signs into a map, and the eyes read it first.
08Tone
How this system expresses tone
Arousal, postural gain, autonomic outflow, and ocular stability share a few centimeters of tissue in this stalk and nowhere else in the body. They share an address, which is why one infarct of a few millimeters takes sympathetic, cerebellar, and spinothalamic function together. Gain, coupling, and set point are the readings this column gives.
Gain
The reticular core decides how much a reflex returns. In 11 human subjects, identical tonic activity in triceps gave a 23.0 percent response during postural support against 3.3 percent isometrically.
Coupling
One medullary field serves pressure and cortex at once. Stimulating it in anesthetized spinalized rats raised cortical blood flow 31 percent and 5 to 6 Hz power 98 percent.
Set point
The pressure the medulla defends moves. In cats a somatic nerve stimulus produced no depressor response until arterial pressure passed 95 mm Hg.
Oscillation: the pre-Bötzinger complex of the ventrolateral medulla generates the breathing rhythm from an identified population of neurokinin 1 receptor cells. Gaze runs its own oscillator a tier above, and a leaking neural integrator shows up at the bedside as nystagmus. Time course: blocking glycine in the rostral ventrolateral medulla of anesthetized rats shortened baroreflex sympathoinhibition from 12 minutes to 5.1 minutes. That field sets how long an answer lasts, not only how large. Prediction: second-order neurons in the vestibular nuclei at the pontomedullary junction tell active head movement from passive head movement, which requires a forecast of the movement the body ordered. Load: the retrotrapezoid nucleus of the rostral medulla holds arterial PCO2 near constant across sleep and waking, and it never stands down. Constraint: the lateral medulla has no spare room. One wedge of infarct took the descending sympathetic pathway in 91 percent of 33 patients, and the cerebellar and spinothalamic pathways in 85 percent each. Input quality: on the floor of the fourth ventricle the vestibular nuclei pool inner-ear, visual, and neck signals and cannot tell which source drove them. A corrupted neck report is read as a report about where the head is.
09Across the library
How this page relates to the rest of the library
The baroreflex worked out beat by beat between the medulla, the cord, and the vessel wall, with the sympathetic and parasympathetic outflows followed to the organs they reach.
The dorsal and ventral respiratory groups, the pontine centers, and the chemoreceptors that feed the rhythm generator located anatomically here.
The nuclei crowding the medullary floor in detail, including the solitary nucleus taking input in and the nucleus ambiguus and dorsal motor nucleus sending output out.
The abducens internuclear neuron that crosses to the contralateral medial rectus subnucleus, and the pupil circuit running through the midbrain tier.
The same stalk before the cortex has any say, when feeding, breathing, and state changes are almost entirely brainstem output.
Heart rate variability, orthostatic testing, and pupillometry as instruments, the two-branch picture corrected, and where the argument over the sacral outflow now stands. Go there for what each autonomic measure can report. Stay here for the medullary fields that produce the outflow.
Dizziness as a clinical state: what provokes an episode, how long one runs, and what the outcome studies show about the treatments that shorten it.
10Frequently asked
Questions about this topic
What does the brainstem do?
The brainstem carries every ascending and descending pathway between the brain and the body, and it houses the nuclei for cranial nerves III through XII. Its reticular core holds arousal and the sleep-wake cycle, sets baseline muscle tone, and shapes posture against gravity. Its medullary centers hold blood pressure, heart rate, and the rhythm of breathing without conscious input. Lesions of the ascending reticular activating system cause coma, which is the plainest demonstration that waking depends on this stalk. Its vestibular nuclei hold the eyes steady while the head moves.
What are the three parts of the brainstem?
The brainstem has three parts: the midbrain, the pons, and the medulla oblongata, stacked from the diencephalon down to the spinal cord. A second arrangement runs the whole length: the tectum behind, the tegmentum in the middle, and the basis in front. The tegmentum holds the cranial nerve nuclei and the reticular formation, and the basis carries the long descending motor tracts. The tectum carries no cranial nuclei, no tracts, and no reticular formation. Knowing both geometries allows a sign to be placed at a tier and a depth.
Which cranial nerves come from the brainstem?
Cranial nerves III through XII arise from brainstem nuclei. The midbrain serves nerves III and IV, the pons serves V through VIII, and the medulla serves IX through XII. Those nuclei sit in the tegmentum just ahead of the fourth ventricle. From the midline outward they run somatic motor, visceral motor, visceral sensory, then somatic sensory. The ascending somatosensory tracts cross the tegmentum in front of them. Cranial nerves I and II are the exceptions, since they are forebrain structures that never enter the stalk.
What happens when the brainstem is damaged?
Damage produces crossed syndromes, where a cranial nerve deficit on one side pairs with a motor or sensory deficit on the other. In 33 patients with lateral medullary infarction, Horner's syndrome appeared in 91 percent, ipsilateral ataxia in 85 percent, and contralateral hypalgesia in 85 percent. Medial medullary infarction reverses the geometry, pairing tongue weakness on the side of the lesion with hemiparesis on the other. Brainstem infarcts account for nearly one third of all ischemic strokes, and medullary infarcts are about 7 percent of ischemic brainstem strokes.
What is the reticular formation?
The reticular formation is a diffuse net of neurons running through the central core of the midbrain, pons, and medulla. Stimulating it in cats abolishes synchronized EEG activity and replaces it with low-voltage fast activity, which is how arousal was first traced to the brainstem. Its pontomedullary portion regulates postural muscle tone through a functional topography, and forebrain and cerebellar efferents converge on it. Human tractography traced that cortical input from most of motor cortex onto the same region. It sets the gain on messages and carries none of them.
What does the brainstem do with a signal it cannot trace to a source?
The brainstem reads it as a report about where the head is. Second-order vestibular neurons at the pontomedullary junction pool inner-ear, visual, and neck proprioceptive input, and they cannot distinguish which source drove them. That pooled reading is what leaves for the eyes and the postural muscles. In humans, rotating the head changes the size of short-latency postural responses attributed to reticulospinal projections, with larger responses contralateral to the direction of rotation. Neck position therefore reaches the same tier that holds gaze, posture, and blood pressure.
How does the Unified Model of Tone read the brainstem?
In the Unified Model of Tone the reticular core holds one organization, and arousal, postural gain, autonomic outflow, and ocular stability are all readings of it. The evidence is convergence at single addresses: 1,065 human diffusion datasets traced most of motor cortex onto the pontomedullary reticular formation, and one medullary field sets cortical blood flow and cortical rhythm together. The model's prediction is that a neck input reaches outputs the contact never touched. In cats, a somatic nerve stimulus lowered blood pressure only when pressure already stood above 95 mm Hg.
How do doctors tell a brainstem stroke from inner-ear dizziness?
A bedside oculomotor examination separates a brainstem stroke from an inner-ear cause. In 101 patients with acute vestibular syndrome, a three-step examination was 100 percent sensitive and 96 percent specific for stroke. Early diffusion-weighted MRI was falsely negative in 12 percent of cases, all within the first 48 hours. Skew deviation carried particular weight, appearing in 30 percent of cases with brainstem involvement against 4 percent of peripheral cases. Vertical and torsional eye signs are the most localizing findings at the bedside, and they cost a penlight and a minute.
11The sources
References
Sources: primary literature, linked inline.