Foundations visual system

CN 3, 4 and 6 _____ the _____

CN 3, 4 and 6 MOVE the EYES

CN 2 (OPTIC) is the nerve of

VISION

pathway of visual stimuli:

cornea → iris (controls amount of light by controlling the pupil) → lens (fine tunes the image) → retina → rods and cones → A focused image will land directly in the center of the macula → fovea

data congregates on the optic disc

Optic Nerve

• All axons converge to form the

• The fibers CROSS at a location known as the _____ _____

• Then split into the R and L ______ ______

• These axons continue and synapse in the ________

• The LGN projects via the _______ ________ to the primary Visual Cortex (Area 17, 18 & 19)

• All axons converge to form the Optic Nerve (CN 2)​

• The fibers CROSS at a location known as the OPTIC CHIASM​

• Then split into the R and L OPTIC TRACT​

• These axons continue and synapse in the THALAMUS​

• The LGN projects via the OPTIC RADIATIONS to the primary Visual Cortex (Area 17, 18 & 19)

Visual Pathway

• Object in RIGHT visual field → Data is transmitted from the

• Temporal fibers DO NOT

• Nasal fibers

• Therefore, the _____ hemisphere receives information about the _____ visual field (and vice versa)

• Object in RIGHT visual field → Data is transmitted from the LEFT half of each retina (temporal portion of LEFT retinal, nasal portion of RIGHT retina) ​

• Temporal fibers DO NOT CROSS → Transmit data to the LEFT Visual Cortex​

• Nasal fibers CROSS → Transmit data to the LEFT Visual Cortex​

• Therefore, the LEFT hemisphere receives information about the RIGHT visual field (and vice versa)

Lesions of the Visual Fields

A. Retinal Lesion:

B. Optic Nerve Lesion: Loss of vision in

C. Optic Chiasm Lesion​

• Loss of vision in ​

• _______ _______​

D. Optic Tract Lesion: ______ ______​

• Loss of vision on

• Temporal loss of the _____ side​

• Nasal loss of the ______ side

A. Retinal Lesion: blind spot in one eye​

B. Optic Nerve Lesion: Loss of vision in one eye​

C. Optic Chiasm Lesion​

• Loss of vision in the temporal half each eye​

• Bitemporal hemianopia​

D. Optic Tract Lesion: Homonymous hemianopia​

• Loss of vision on one half of each eye​

• Temporal loss of the SAME side​

• Nasal loss of the OPPOSITE side

Localization

• Frontal

• Parietal

• Occipital

• Temporal

• Frontal

  • movement, higher order cognition, decision making and planning, language

• Parietal

  • processing and integration of sensory input

• Occipital

  • vision

• Temporal

  • hearing, learning, and memory

Lateralization

• L hemisphere

• R hemisphere

• L hemisphere

  • generally considered the dominant hemisphere

  • language

• R hemisphere

  • non-dominant

  • non-verbal

  • complex visual-spatial skills

Localization & Lateralization

• Focal brain lesions can cause specific deficits BUT not all lesions are created equally.​

• ______ _______ plays a role in the way a lesion affects an individual

• Ex: MCA

• Hemispheric Specialization

Example of Lateralization

• 90% of the population is R handed​

  • Skilled, complex motor tasks are more detailed in the dominant hemisphere​

  • Lesions in the dominant hemisphere →

• 90% of the population is R handed​

  • Skilled, complex motor tasks are more detailed in the dominant hemisphere​

  • Lesions in the dominant hemisphere → Apraxia

Association Cortices

• Frontal Lobe​

• Parietal Lobe​

• Occipital Lobe​

• Temporal Lobe​

• Frontal Lobe​

  • Frontal/prefrontal association cortex (Areas 9 - 12)​

  • Motor/Primary Motor association cortex (Areas 4, 6 and 8)​

  • Language Association Area (Broca, 44, 45)​

• Parietal Lobe​

  • Primary Somatosensory cortex (3, 1, 2)​

  • Somatosensory association cortex (Area 5, 7)​

  • Lateral parietal and temporal heteromodal association cortex (39, 40)​

• Occipital Lobe​

  • Visual association cortex (Areas 17, 18, 19)​

• Temporal Lobe​

  • Auditory Association Cortex (Wernicke’s Area, 22)​

  • Primary Auditory Cortex (41, 42)

Symptoms of frontal lobe dysfunction

• Perseveration​

  • “stuck in a loop”

  • don’t have mental flexibility

• Difficulty with abstract reasoning​

• Disinhibition​

• Disorders of Attention​

  • Focused attention → Focusing on a particular object above others​

  • Sustained attention → Vigilance, concentration, non-distractibility

Language and communication areas

• Language and communication areas are distributed between both the

• Frontal Lobe: Area 44, 45 →

• Temporal Lobe: Area 22 →

• Language and communication areas are distributed between both the frontal and temporal lobes​

• Frontal Lobe: Area 44, 45 → Language association Area​

• Temporal Lobe: Area 22 → Auditory association area

Language and Communication

• Left Hemisphere: Dominant for language in > _____ of right handed people and ____ – ____ of left handed people​

• Lesions of the Left hemisphere →

• Wernicke’s Area: (Area 22):

  • Deficit here:

• Broca’s Area (Area 44 & 45):​

  • Deficit here:

• Left Hemisphere: Dominant for language in > 95% of right handed people and 60 – 70% of left handed people​

• Lesions of the Left hemisphere → Language disorders​

• Wernicke’s Area: (Area 22):

  • Deficit here: Receptive Aphasia​

• Broca’s Area (Area 44 & 45):

  • Deficit here: Expressive aphasia

Broca’s (Non-Fluent, Expressive Aphasia)

• Good comprehension​

• Awkward articulation, restricted vocabulary, restriction to simple grammatical forms​

• Reading may be somewhat less impaired than speech and writing

Receptive (Wernicke’s) Aphasia

• Poor naming skills, poor reading comprehension, poor writing skills​

• Speech is fluent, but marked by word substitutions and neologisms (nonsense words)​

• Speech may also be at a faster rate than normal

Visual Deficits

• Motor Deficit: Problem with

• Sensory Deficit: Problem with getting the data from the

• Perceptual​

• Motor Deficit: Problem with Oculomotor control, eye movement​

• Sensory Deficit: Problem with getting the data from the eye to the visual cortex​

  • Homonymous hemianopia​

  • Bitemporal hemianopia​​

• Perceptual​

  • Interpretation, recognition and memory at the cortical level 

Visual Object Agnosia

• Lesion in areas

• Usually

• DEF: Inability to

• Language and general intellectual functions are

• “Recognition without _______”

• Lesion in areas 18 and 19​

• Usually bilateral​

• DEF: Inability to name, copy or recognize a visually presented object, face or even sometimes letters​

• Language and general intellectual functions are preserved​

• “Recognition without meaning”

Facial Agnosia: Prosopagnosia

• Unable to recognize

  • Must identify by

• Can recognize the parts of a face and that a face is a face, but, cannot assign _______ to a face in the form of a Name​

• Caused by deficits in the ______ lobe where it meets the _______ lobe on the ventral surface of the brain ==> The fusiform gyrus​

• This lesion is usually _______ to result in the deficit

• Unable to recognize faces​

  • Must identify by voice or other cues​

• Can recognize the parts of a face and that a face is a face, but, cannot assign MEANING to a face in the form of a Name​

• Caused by deficits in the occipital lobe where it meets the temporal lobe on the ventral surface of the brain ==> The fusiform gyrus​

• This lesion is usually BILATERAL to result in the deficit

Parietal Association Areas

• Parietal Association Cortex: At the junction of the parietal, temporal and occipital lobes (Areas ___,___)​

• Especially important for _____ _____ → Especially the R (non-dominant) ​

• Analyzes the location and movement of visual objects in _____​

• This spatial analysis requires large amounts of data:​

• Parietal Association Cortex: At the junction of the parietal, temporal and occipital lobes (Areas 39, 40)​

• Especially important for spatial analysis → Especially the R (non-dominant) ​

• Analyzes the location and movement of visual objects in space​

• This spatial analysis requires large amounts of data:​

  • Visual​

  • Proprioceptive​

  • Vestibular​

  • Auditory

Lesion: R Parietal Area

Hemineglect Syndrome

• Most often occurs with infarcts in the R parietal or R frontal lobe​

• ”Neglect” of the contralateral side of the “world” – varies in severity​

• Often accompanied with a complete lack of awareness of this deficit