Secondary Visual Cortex

Secondary Visual Cortex

Introduction

<table class="infobox infobox-cell">
<tr>
<th class="infobox-header" colspan="2">Secondary Visual Cortex</th>
</tr>
<tr>
<td class="label">Category</td>
<td>Visual Cortex, Ventral Stream</td>
</tr>
<tr>
<td class="label">Location</td>
<td>Occipital lobe, surrounding primary visual cortex (V1)</td>
</tr>
<tr>
<td class="label">Brodmann Areas</td>
<td>BA 18 (secondary), BA 19 (associative visual cortex)</td>
</tr>
<tr>
<td class="label">Function</td>
<td>Complex visual feature processing, form perception, depth analysis</td>
</tr>
<tr>
<td class="label">Key Inputs</td>
<td>Primary visual cortex (V1)</td>
</tr>
<tr>
<td class="label">Key Outputs</td>
<td>V4, IT cortex, posterior parietal cortex</td>
</tr>
</table>

Secondary Visual [Cortex](/brain-regions/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.

Secondary Visual Cortex

Introduction

<table class="infobox infobox-cell">
<tr>
<th class="infobox-header" colspan="2">Secondary Visual Cortex</th>
</tr>
<tr>
<td class="label">Category</td>
<td>Visual Cortex, Ventral Stream</td>
</tr>
<tr>
<td class="label">Location</td>
<td>Occipital lobe, surrounding primary visual cortex (V1)</td>
</tr>
<tr>
<td class="label">Brodmann Areas</td>
<td>BA 18 (secondary), BA 19 (associative visual cortex)</td>
</tr>
<tr>
<td class="label">Function</td>
<td>Complex visual feature processing, form perception, depth analysis</td>
</tr>
<tr>
<td class="label">Key Inputs</td>
<td>Primary visual cortex (V1)</td>
</tr>
<tr>
<td class="label">Key Outputs</td>
<td>V4, IT cortex, posterior parietal cortex</td>
</tr>
</table>

Secondary Visual [Cortex](/brain-regions/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. [@kandel2013]

Overview

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

• 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

Cytoarchitecture

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

• Small granule cells
• Receives thalamic inputs (sparse in V2)

• Medium pyramidal neurons
• Primary source of corticocortical projections
• Strong horizontal connections within V2

• Less prominent than in V1
• Receives input from V1
• Contains stellate cells

• Large pyramidal neurons
• Projects to superior colliculus and pulvinar
• Subcortical motor-related projections

• Mixed neuron types
• Projects to thalamus (feedback connections)

Columnar Organization

V2 maintains a columnar organization similar to V1:

Orientation Columns:

• [Neurons](/entities/neurons) grouped by preferred orientation
• Similar to V1 but with differences in column spacing
• Systematic representation of visual space

• Less pronounced than in V1
• Input from both eyes integrated at this level
• Binocular fusion begins in V2

• Color-selective blobs present but less prominent
• Interblob regions process form and shape
• Continued segregation of functional streams

Functional Organization

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

• Motion perception
• Spatial location
• Visuomotor coordination
• Action guidance

Receptive Field Properties

V2 neurons have larger receptive fields than V1 neurons:

Simple Cells:

• Oriented edge detectors
• Specific position within receptive field
• Responds to light/dark edges

• Orientation-selective
• Less position-specific
• Responds to moving edges

• Responds to lines of specific length
• Detects corners and curves
• Important for contour integration

Specialization for Complex Features

V2 neurons are tuned to more complex visual features than V1:

Curvature and Contour:

• Curved edge detectors
• Contour integration neurons
• Shape from shading

• Surface curvature
• Relative depth
• Occlusion boundaries

• Boundary detection
• Surface segregation
• Contextual influences

Connectivity

Inputs

V2 receives input from multiple sources:

From V1:

• The primary source of visual information
• Spreads across all layers
• Preserves retinotopic organization

• Pulvinar nucleus (feedback)
• Lateral geniculate nucleus (sparse)
• Modulatory rather than driving

• V3 (feedback)
• MT (motion information)
• Auditory and somatosensory (multisensory integration)

Outputs

V2 projects to several higher visual areas:

Major Targets:

• V4 (color and form)
• Inferotemporal cortex (object recognition)
• MT (motion)
• Posterior parietal cortex (spatial)

• Superior colliculus (attention)
• Pulvinar (attention)
• Pretectal nucleus (pupil reflex)

Horizontal Connections

V2 has extensive horizontal connections:

Intrinsic Connections:

• Links columns of similar function
• Spans 2-4 mm horizontally
• Mediated by layer 2/3 pyramidal cells

• Contextual modulation
• Surface completion
• Illusion perception

Role in Visual Perception

Form and Shape Processing

V2 is crucial for processing complex shapes:

Contour Integration:

• Grouping of edge segments
• Border ownership
• Surface filling-in

• Curvature processing
• Angular detection
• Complex pattern recognition

Depth Perception

V2 contributes to 3D vision:

Binocular Disparity:

• Fine disparity tuning
• Stereo depth perception
• Relative depth judgment

• 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

• Luminance contrast
• Lightness constancy
• Surface reflectance

Clinical Relevance

Posterior Cortical Atrophy

Posterior Cortical Atrophy (PCA), often due to [Alzheimer's disease](/diseases/alzheimers-disease), prominently affects V2:

Symptoms:

• Visual perception deficits
• Reading difficulties
• Object recognition impairment
• Spatial disorientation

• Neurodegeneration in posterior cortical areas
• Includes V2 as early target
• [Beta-amyloid](/proteins/amyloid-beta) and [tau](/proteins/tau) pathology

Alzheimer's Disease

V2 involvement in AD extends beyond PCA:

Early Changes:

• Hypometabolism in posterior cortices
• Functional disconnection from V1
• Synaptic loss in layer 2/3

• Visual processing deficits
• Difficulty with complex scenes
• Impaired navigation

Visual Hallucinations

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

• Partial recovery common
• V1 lesions have worse prognosis
• Plasticity within V2 can compensate

Experimental Findings

Neurophysiology Studies

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

• 1-3 degrees at fovea
• Increase with eccentricity
• Larger than V1 (5-10x)

Imaging Studies

fMRI in humans has confirmed V2 organization:

retinotopic Mapping:

• Clear retinotopic organization
• Multiple visual areas identified
• Dorsal/ventral stream segregation

• Complex shape processing
• Contour integration
• Surface perception

Connectional Studies**

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

Developmental Timeline

V2 develops over an extended postnatal period:

Critical Period:

• Extends into adolescence
• Experience-dependent refinement
• Binocular competition

• Myelination complete by age 12
• Synaptic pruning continues
• Columnar organization refines

Plasticity in Adults

V2 retains some capacity for modification:

Training Effects:

• Expert perception (carpenters, bird watchers)
• Perceptual learning
• Multisensory integration changes

• Partial reorganization possible
• Depends on extent of damage
• Rehabilitation can enhance recovery

Research Directions

Decoding Visual Perception

V2 activity can be used to decode visual experiences:

Brain-Machine Interfaces:

• Visual prosthesis development
• Artificial vision
• Neural coding research

• Neural correlates of consciousness
• Perceptual inference
• Predictive coding

Computational Models

V2 is a focus of computational neuroscience:

Neural Network Models:

• Hierarchical processing
• Recurrent connections
• Attention mechanisms

• Predictive coding theories
• Hierarchical Bayesian inference
• Efficient coding hypotheses

Related Pages

• [Primary Visual Cortex (V1)visual-cortex-v1)
• [Visual Cortex V4](/cell-types/visual-cortex-v4)
• [Inferior Temporal Cortex](/cell-types/inferior-temporal-cortex)
• [Posterior Cortical Atrophy](/diseases/posterior-cortical-atrophy)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Visual Processing](/mechanisms/visual-processing)
• [Dorsal Visual Stream](/mechanisms/dorsal-visual-stream)
• [Ventral Visual Stream](/mechanisms/ventral-visual-stream)

Background

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.

See Also

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Amyloid Hypothesis](/mechanisms/amyloid-hypothesis)
• [Tau Pathology](/mechanisms/tau-pathology)
• [/mechanisms/app-processing](/mechanisms/app-processing)
• [/mechanisms/amyloid-aggregation](/mechanisms/amyloid-aggregation)

External Links

• [Neuroscience - Secondary Visual Cortex](https://www.neuroscience.com/)
• [Allen Brain Atlas - Visual Cortex](https://brain-map.org/)
• [Human Connectome Project](https://www.humanconnectome.org/)