Secondary Visual Cortex is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
The secondary visual cortex, also known as V2 or the prestriate cortex, is a critical region in the ventral visual stream of the mammalian brain. Located immediately posterior to the primary visual cortex (V1), V2 receives processed visual information from V1 and performs more complex visual processing, including the analysis of object features, spatial relationships, and contextual information. This page provides a comprehensive overview of V2 anatomy, function, connectivity, and its relevance to neurodegenerative diseases.
| Property |
Value |
| Category |
Visual Cortex, Ventral Stream |
| Location |
Occipital lobe, surrounding primary visual cortex (V1) |
| Brodmann Areas |
BA 18 (secondary), BA 19 (associative visual cortex) |
| Function |
Complex visual feature processing, form perception, depth analysis |
| Key Inputs |
Primary visual cortex (V1) |
| Key Outputs |
V4, IT cortex, posterior parietal cortex |
The secondary visual cortex represents approximately 10-15% of the total neocortex in primates and contains a highly organized columnar architecture similar to V1. V2 is essential for constructing our perceptual experience of the visual world, integrating basic visual features into coherent representations of objects and scenes.
¶ Anatomy and Structure
¶ Location and Boundaries
V2 occupies the banks of the lunate sulcus and the superior and inferior occipital sulci in the occipital lobe:
Boundaries:
- Anterior: Primary visual cortex (V1, BA 17)
- Posterior: Tertiary visual areas (V3, V4)
- Superior: Parietal-occipital sulcus boundary
- Inferior: Occipitotemporal sulcus
Thickness:
- V2 cortex is approximately 2-2.5 mm thick
- Layer 4 (external granular layer) is less prominent than in V1
- Layer 2/3 contains numerous small pyramidal neurons
V2 exhibits a six-layered neocortical organization with some distinctive features:
Layer I (Molecular Layer):
- Sparse cell bodies
- Dendritic processes and axons
- Few inhibitory interneurons
Layer II (External Granular Layer):
- Small granule cells
- Receives thalamic inputs (sparse in V2)
Layer III (External Pyramidal Layer):
- Medium pyramidal neurons
- Primary source of corticocortical projections
- Strong horizontal connections within V2
Layer IV (Internal Granular Layer):
- Less prominent than in V1
- Receives input from V1
- Contains stellate cells
Layer V (Internal Pyramidal Layer):
- Large pyramidal neurons
- Projects to superior colliculus and pulvinar
- Subcortical motor-related projections
Layer VI (Multiform Layer):
- Mixed neuron types
- Projects to thalamus (feedback connections)
¶ Columnar Organization
V2 maintains a columnar organization similar to V1:
Orientation Columns:
- Neurons grouped by preferred orientation
- Similar to V1 but with differences in column spacing
- Systematic representation of visual space
Ocular Dominance Columns:
- Less pronounced than in V1
- Input from both eyes integrated at this level
- Binocular fusion begins in V2
Blob/Interblob Domains:
- Color-selective blobs present but less prominent
- Interblob regions process form and shape
- Continued segregation of functional streams
¶ Ventral and Dorsal Streams
V2 is a critical hub in both the ventral ("what") and dorsal ("where") visual streams:
Ventral Stream (V1 → V2 → V4 → IT):
- Object identification and recognition
- Color and form perception
- Detailed shape analysis
- Consciousness and recognition
Dorsal Stream (V1 → V2 → MT → VIP/MST):
- Motion perception
- Spatial location
- Visuomotor coordination
- Action guidance
V2 neurons have larger receptive fields than V1 neurons:
Simple Cells:
- Oriented edge detectors
- Specific position within receptive field
- Responds to light/dark edges
Complex Cells:
- Orientation-selective
- Less position-specific
- Responds to moving edges
End-stopped Cells:
- Responds to lines of specific length
- Detects corners and curves
- Important for contour integration
V2 neurons are tuned to more complex visual features than V1:
Curvature and Contour:
- Curved edge detectors
- Contour integration neurons
- Shape from shading
3D Surface Properties:
- Surface curvature
- Relative depth
- Occlusion boundaries
Figure-Ground Segmentation:
- Boundary detection
- Surface segregation
- Contextual influences
V2 receives input from multiple sources:
From V1:
- The primary source of visual information
- Spreads across all layers
- Preserves retinotopic organization
From Thalamus:
- Pulvinar nucleus (feedback)
- Lateral geniculate nucleus (sparse)
- Modulatory rather than driving
From Other Cortical Areas:
- V3 (feedback)
- MT (motion information)
- Auditory and somatosensory (multisensory integration)
V2 projects to several higher visual areas:
Major Targets:
- V4 (color and form)
- Inferotemporal cortex (object recognition)
- MT (motion)
- Posterior parietal cortex (spatial)
Subcortical Outputs:
- Superior colliculus (attention)
- Pulvinar (attention)
- Pretectal nucleus (pupil reflex)
V2 has extensive horizontal connections:
Intrinsic Connections:
- Links columns of similar function
- Spans 2-4 mm horizontally
- Mediated by layer 2/3 pyramidal cells
Functional Implications:
- Contextual modulation
- Surface completion
- Illusion perception
V2 is crucial for processing complex shapes:
Contour Integration:
- Grouping of edge segments
- Border ownership
- Surface filling-in
Shape Recognition:
- Curvature processing
- Angular detection
- Complex pattern recognition
V2 contributes to 3D vision:
Binocular Disparity:
- Fine disparity tuning
- Stereo depth perception
- Relative depth judgment
Monocular Depth Cues:
- Linear perspective
- Texture gradients
- Occlusion
¶ Color and Brightness
While V4 is primary for color, V2 contributes:
Color Processing:
- Some color-selective neurons
- Color contrast enhancement
- Surface color perception
Brightness Perception:
- Luminance contrast
- Lightness constancy
- Surface reflectance
Posterior Cortical Atrophy (PCA), often due to Alzheimer's disease, prominently affects V2:
Symptoms:
- Visual perception deficits
- Reading difficulties
- Object recognition impairment
- Spatial disorientation
Pathology:
- Neurodegeneration in posterior cortical areas
- Includes V2 as early target
- Beta-amyloid and tau pathology
V2 involvement in AD extends beyond PCA:
Early Changes:
- Hypometabolism in posterior cortices
- Functional disconnection from V1
- Synaptic loss in layer 2/3
Clinical Correlates:
- Visual processing deficits
- Difficulty with complex scenes
- Impaired navigation
V2 dysfunction may contribute to visual hallucinations in Lewy body disease:
Mechanisms:
- Visual pathway degeneration
- Disinhibition of visual cortex
- Cholinergic deficiency
¶ Stroke and Lesions
Occipital lobe strokes affecting V2 cause characteristic deficits:
Deficits:
- Visual form agnosia
- Akinetopsia (motion blindness)
- Color blindness
- Depth perception impairment
Recovery:
- Partial recovery common
- V1 lesions have worse prognosis
- Plasticity within V2 can compensate
Single-unit recordings in primates have revealed V2 properties:
Feature Selectivity:
- 60-70% orientation-selective neurons
- 20-30% direction-selective neurons
- 10-15% color-selective neurons
Receptive Field Sizes:
- 1-3 degrees at fovea
- Increase with eccentricity
- Larger than V1 (5-10x)
fMRI in humans has confirmed V2 organization:
** retinotopic Mapping:**
- Clear retinotopic organization
- Multiple visual areas identified
- Dorsal/ventral stream segregation
Functional Activation:
- Complex shape processing
- Contour integration
- Surface perception
Tracing studies have mapped V2 connectivity:
Hierarchical Position:
- V2 is second tier of visual hierarchy
- Major hub between V1 and higher areas
- Integrates multiple information streams
¶ Development and Plasticity
V2 develops over an extended postnatal period:
Critical Period:
- Extends into adolescence
- Experience-dependent refinement
- Binocular competition
Maturation:
- Myelination complete by age 12
- Synaptic pruning continues
- Columnar organization refines
V2 retains some capacity for modification:
Training Effects:
- Expert perception (carpenters, bird watchers)
- Perceptual learning
- Multisensory integration changes
Recovery from Injury:
- Partial reorganization possible
- Depends on extent of damage
- Rehabilitation can enhance recovery
V2 activity can be used to decode visual experiences:
Brain-Machine Interfaces:
- Visual prosthesis development
- Artificial vision
- Neural coding research
Cognitive Neuroscience:
- Neural correlates of consciousness
- Perceptual inference
- Predictive coding
V2 is a focus of computational neuroscience:
Neural Network Models:
- Hierarchical processing
- Recurrent connections
- Attention mechanisms
Theoretical Frameworks:
- Predictive coding theories
- Hierarchical Bayesian inference
- Efficient coding hypotheses
The study of Secondary Visual Cortex has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- Van Essen DC, Felleman DJ, DeYoe EA, Olavarria J, Knierim J. Modular organization of extrastriate cortex in the macaque monkey. Cold Spring Harb Symp Quant Biol. 1990;55:679-694. PMID:2134686
- Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 5th ed. McGraw-Hill; 2013.
- Goodale MA, Milner AD. Separate visual pathways for perception and action. Trends Neurosci. 1992;15(1):20-25. PMID:1374953
- Ungerleider LG, Mishkin M. Two cortical visual systems. In: Ingle DJ, Goodale MA, Mansfield RJW, eds. Analysis of Visual Behavior. MIT Press; 1982:549-586.
- Zeki S. The visual cortex: descriptions and the machine. J Neural Eng. 2004;1(4):R1-R9. PMID:15578141
- Nassi JJ, Callaway EM. Parallel processing strategies of the primate visual system. Nat Rev Neurosci. 2009;10(5):360-372. PMID:19377503
- Livingstone M, Hubel D. Segregation of form, color, movement, and depth: anatomy, physiology, and perception. Science. 1988;240(4853):740-749. PMID:3283936
- Schott GD, ed. Imaging the Brain in Neurological and Psychiatric Disorders. Oxford University Press; 2014.
- Crutch SJ, Lehmann M, Schott JM, Rabinovici GD, Rossor MN, Fox NC. Posterior cortical atrophy: discordant neurodegenerative and psychiatric symptoms. J Neurol Neurosurg Psychiatry. 2012;83(5):519-521. PMID:22334027
10.Ffytche DH. The Hodology of Hallucinations. Cortex. 2008;44(8):1067-1083. PMID:18599210