cortical eye movements

Frontal lobe

1. Frontal Lobe

   • Prefrontal Cortex: Involved in high-level functions like abstract thinking, decision-making, and anticipation.

   • Frontal Eye Field (FEF): Controls voluntary saccades (quick eye movements to shift gaze) and suppresses reflexive saccades.

     • Smooth Pursuits: secondary role - not origin maintains smooth pursuit movements (following a moving object).

Parietal Lobe

• Integrates sensory information crucial for navigation and attention.

• Righting Reflex and Sensation: Important for body balance.

• Saccades and Smooth Pursuits: Reflexive saccades are also modulated here.

• Optic Radiations: Carries visual information from the occipital cortex

temporal lobe

• Handles memory, sound recognition, and speech processing.

• Contributes to Attention in oculomotor control.

• Optic Radiations: Another pathway for visual processing.

Occipital Lobe

• Primary Visual Cortex (V1 - Area 17): Receives and begins processing visual information.

• Secondary Visual Areas (V2-V4): Handles more complex processing like color, motion, and spatial localization.

limbic lobe

Hippocampus, Amygdala, Anterior Thalamic Nuclei: Involved in emotion, memory, and behavior that may influence attention and gaze behaviors.

Pathways and Tracts

Internal Capsule: A major white matter pathway that carries signals between the cortex and brainstem.

• Corticospinal Tract: Facilitates motor signal transfer, part of internal capsule extending downwards.

• Optic Radiations: Transmit visual information from the thalamus to the occipital lobe.

Brodmann Areas Relevant to Eye Movements

• Primary Motor Area (4): Executes voluntary movement.

• Premotor Cortex (6): Coordinates movement planning.

• Frontal Eye Field (8): Controls saccades and smooth pursuits.

• Primary Visual Area (17) and Association Visual Areas (18, 19): Crucial for visual processing and initial visual inputs for movement.

midbrain - eye movements

1. Midbrain

   • RiMLF (Rostral Interstitial Nucleus of MLF): Controls vertical saccades.

   • Superior Colliculus: Processes reflexive saccades; visual sensory integration.

   • Substantia Nigra: Modulates eye movement, with a role in reward and inhibition.

   • INC

   • Posterior commisure

Vergence

• mesencephalic reticular formation

pons

• Horizontal saccades - PPRF (Paramedian Pontine Reticular Formation): Generates horizontal saccades.

• Abducens Nucleus (VI): Controls lateral gaze and sends internuclear neurons to the MLF.

• Smooth persuit - Dorsolateral Pontine Nuclei: Coordinates smooth pursuits with cerebellum.

• Vergence - nucleus reticularis tegmenti pons

medulla

Nucleus Prepositus Hypoglossi: Integrates saccadic movement, particularly for horizontal gaze.

Cerebellum's Role in Eye Movements

• Flocculus: Integrates smooth pursuit eye movements.

• Vermis: Involved in saccades.

• Cerebellar Peduncles: Main communication route between the brainstem and cerebellum.

pathway for Saccades

1. Saccades

   • Amplitude: Controlled by lower motor neurons.

   • Direction: Determined by premotor neurons (PPRF and RiMLF).

   • Speed (Pulse): Phasic command from burst cells (e.g., NPCC).

   • Hold (Step): Tonic signal from integrator cells (e.g., NPH).

Vergence and Gaze Control

• Vergence and Gaze Control

  • Vestibulo-Ocular Reflex (VOR): Stabilizes vision during head movement by sending counter-rotating commands.

  • Vergence Movements: Coordinated by mesencephalic reticular formation, NRTP, and cranial nerves III and VI.

smooth persuit

Smooth pursuit movements allow the eyes to track slow-moving objects smoothly to maintain fixation on a moving target.

Pathway:

1. Visual Input →retina→ optic nerve →primary visual cortex (V1) in the occipital lobe.

2. Movement processed → middle temporal (MT) visual cortex &medial superior temporal (MST) visual area.

3. Frontal Eye Field (FEF) →frontal lobe → parietal eye fields and cerebellum.

4. Signals are sent → pontine nuclei in brainstem → cerebellum (especially the flocculus and vermis)

5. Cerebellum sends signals→Vestibular nuclei→ ocular motor nuclei (III, IV, VI) via → (MLF) to drive coordinated eye movement.

Clinical Relevance:

• Defects in smooth pursuit are often associated with:

  • Cerebellar disease: Ataxic or jerky pursuit.

  • Parietal lobe lesions: Difficulty initiating or maintaining pursuit.

  • Vestibular disorders: Impaired integration with cerebellar and ocular motor systems.

saccades

Saccades are rapid, ballistic eye movements that allow the eyes to quickly shift fixation from one target to another.

Pathway:

1. Begins → visual stimuli or voluntary decision → frontal eye fields (FEF) in → frontal lobe for voluntary saccades.

   • Reflexive saccades are initiated in the parietal eye fields and superior colliculus.

2. Signal Relay to Brainstem:

   • The FEF sends signals → superior colliculus and basal ganglia.

   • Horizontal Saccades → paramedian pontine reticular formation (PPRF) in → pons.

     • Signals from the PPRF → (VI) nucleus.

     • The abducens activates → ipsilateral LR and sends signals → MLF to the contralateral oculomotor (III) nucleus to activate MR

   • Vertical Saccades →rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in the midbrain.

     • Signals activate the superior and inferior rectus and oblique muscles.

3. Motor Execution:

   • The signal reaches → (III, IV, VI), generating the rapid movement.

Clinical Relevance:

• Slowed or impaired saccades occur with:

  • Basal ganglia diseases (e.g., Parkinson’s): Difficulty initiating saccades.

  • PPRF lesions: Impaired horizontal saccades.

  • riMLF lesions: Impaired vertical saccades.

• Hypermetric or hypometric saccades suggest cerebellar dysfunction.

saccadic pathway

Voluntary

cortical areas

FEF & Parietal lobe & secondary visual area

• Visual Cortex → Posterior Parietal Cortex → FEF.

• FEF → Internal Capsule → Caudate Nucleus →Substantia Nigra → Superior Colliculus → Cerebellum.

• Cerebellum → Brainstem nuclei for final execution: via INC or NPH via 8th - cerebellum

  • Horizontal: PPRF → 6th Nerve (Abducens) → MLF → 3rd Nerve (Oculomotor).

  • Vertical: RiMLF → 3rd & 4th Nerves via INC and NPH

Reflexive

-visual cortex → posterior parietal cortex → superior colliculus - brainstem nuclei

• horizontal - PPRF - 6th & 3rd - via MLF

• vertical - RiMLF - 3rd & 4th downward

internal capsule - basal ganglia, superior colliculi, Pednuculppontine patway - cerebellum - 3rd for horizontal gaze

Horizontal

• PPRF - pons, NPCC= saccadic movement

• NRI = pause cells

• 6th nerve & 3rd nerve - brainstem via MLF

• NPH & medial 8th nucleus

Vertical

• RiMLF -

• 3rd and 4th

• INC & MEDIAL 8TH nucleus

FEF → Internal capsule → caudate nuclei → superior colliculi → substanstia Nigra → cerebellum → brainstem nuclei

1. → vertical RiMLF → 3rd & 6th

2. INC - NPH → 8th medial cerebellum

3. Horizontal

   • PPRF →6th

   • NRI → 3rd

anatomy

• visual cortex - posterior parietal lobe - FEF - Caudate nucleus & superior colliculus -

• substantia nigra - superior colliculus - brainstem - brainstem nuclei

• reflexive -

reflexive

visual cortex → posteior pariteal cortex → superior collicolus

superior colliculus - reflexive saccades

substantia nigra - voluntary saccades

SP

Cortical areas:

Occipital lobe - striate cortex

MST/ MT - temporal lobe - secondary visual area v5

Pareital lobe

FEF

Cortex →internal capsule → midbrain & pons → DPLN → cerebellum (flocullus & vermis) →vestibular nuclei

Brainstem nuclei

Horizontal

• direct from cerebellum & DPLN = 6th = LR

• 6th and 3rd

Vertical SP

• from cerebellum, vestibular nuclei & pons to 3 & 4th

1. Visual input: Occipital lobe (striate cortex) → Secondary visual areas (V5: MT and MST).

2. Motion signal relay: MT/MST → DLPN → FEF (initiates pursuit).

3. Coordination and fine-tuning: FEF → Cerebellum (flocculus/vermis) → Vestibular nuclei.

4. Execution:

   • Horizontal: 6th nucleus → lateral rectus + 3rd nucleus → medial rectus.

   • Vertical: 3rd and 4th nuclei control vertical eye muscles

VOR

Head velocity & movement

semicircular canals

Otolith organs

vestibular nerve - vestibular nuclei - cerebellum - oculomotor nuclei

• 3rd

• 4th

• 6th

Opto-kinetic(OKN) - quick response when VOR not working - visual input - via mossy fibres - inferior olivary nucleus via climbing fibres - cerebellum - flocculus & ventral parafloccolus - brainstem nuclei

Vergence movement + gaze control

Cortical areas

FEF

PEF

MT/MST

NRTP → Cerebellum (dorsal, vermis, flocculus, fatigal nucleus) → MRF

• 3rd NN - convergence - medial recti + pupil miosis + accom

• 6th - Divergence - pupil mydriasis + accom

Horizontal

• contralateral MR → MLF → 6th - ipsilaterial LR

vertical

• 3rd → 4th via

• bilateral input w communication via posterior commisure