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Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins
Neuroscience: Exploring the
Brain, 3e
Chapter 10: The Central Visual System
FARVARDIN NEURO-COGNITIVE TRAINING GROUP

Introduction
• Neurons in the visual system
– Neural processing results in perception
• Parallel pathway serving conscious visual perception
originate in the retina
– Progress to lateral geniculate nucleus, primary visual
cortex & higher order visual areas in temporal and
parietal lobes
• Overlapping neuronal receptive fields
– Sensitive to different facets of the visual input

The Retinofugal Projection
• The Optic Nerve, Optic Chiasm, and Optic Tract

• Right and Left Visual Hemifields
– Left hemifield projects to right side of brain
– Ganglion cell axons from nasal retina cross, temporal
retinal axons stay ipsilateral

• Visual deficits from lesions in the retinofugal projection

• Nonthalamic Targets of the Optic Tract:
– Hypothalamus: Biological rhythms, including
sleep and wakefulness
– Pretectum: Size of the pupil; certain types of
eye movement
– Superior colliculus: Orients the eyes in response
to new stimuli

The Lateral
Geniculate
Nucleus
(LGN)

The Lateral Geniculate Nucleus (LGN)
• Inputs Segregated by Eye and Ganglion Cell Type

• Receptive Fields
– Receptive fields of LGN neurons: Identical to the
ganglion cells that feed them
– Magnocellular LGN neurons: Large, monocular
receptive fields with transient response
– Parvocellular LGN cells: Small,monocular
receptive fields with sustained response

• Nonretinal Inputs to the LGN
– Primary visual cortex provides 80% of the synaptic
input to the LGN
– Brain stem neurons provide modulatory influence on
neuronal activity

Anatomy
of the
Striate
Cortex

Anatomy of the Striate Cortex
• Retinotopy
– Map of the visual field onto a target structure (retina,
LGN, superior colliculus, striate cortex)
– Central visual field overrepresented
– Discrete point of light: Activates many cells in the target
structure due to overlapping receptive fields
– Perception: Based on the brain’s interpretation of
distributed patterns of activity

• Retinotopy

• Lamination of the Striate Cortex
– Layers I - VI
– Spiny stellate cells: Spine-
covered dendrites; layer IVC
– Pyramidal cells: Spines; thick
apical dendrite;
layers III, IVβ, V, VI
– Inhibitory neurons: Lack
spines; All cortical layers;
Form local connections

• Inputs to the Striate Cortex
– Magnocellular LGN neurons: Project to layer IVCα
– Parvocellular LGN neurons: Project to layer IVCβ
– Koniocellular LGN axons: Bypasses layer IV to make
synapses in layers II and III

• Ocular Dominance Columns
– Studied with transneuronal autoradiography from retina,
to LGN, to striate cortex.

• Ocular Dominance Columns
– Present in layer IV of macaque monkeys - alternating
inputs from two eyes

• Inputs to the Striate Cortex
– First binocular neurons found in striate cortex - most layer
III neurons are binocular (but not layer IV)

• Outputs of the Striate Cortex:
– Layers II, III, and IVB:
Projects to other cortical areas
– Layer V: Projects to the
superior colliculus and pons
– Layer VI: Projects back to the
LGN

Physiology of the Striate Cortex
• Monocular Receptive Fields
– Layer IVC: Similar to LGN cells
– Layer IVCα: Insensitive to the wavelength
– Layer IVCβ: Center-surround color opponency
• Binocular Receptive Fields
– Layers superficial to IVC: First binocular receptive
fields in the visual pathway
– Two receptive fields - one for each eye

• Cortical Receptive Fields
– Orientation Selectivity

– Direction Selectivity
• Neuron fires action potentials in response to
moving bar of light

– Simple cells: Binocular; Orientation-selective;
Elongated on-off region with antagonistic flanks
responds to optimally oriented bar of light
– Possibly composed of three LGN cell axons with
center-surround receptive fields

– Complex cells: Binocular; Orientation-selective; ON
and OFF responses to the bar of light but unlike
simple cells, no distinct on-off regions

– Blob Receptive Fields:
• Circular
• Monocular
• No orientation or direction selectivity
• Majority of color-sensitive neurons outside
layer IVC
• Specialized for analysis of object color

• Parallel Pathways: Magnocellular; Koniocellular;
Parvocellular

• Cortical Module
– Each module capable of analyzing every aspect
of a portion of the visual field

Beyond Striate Cortex
• Dorsal stream
– Analysis of visual motion and
the visual control of action
• Ventral stream
– Perception of the visual world
and the recognition of objects

• The Dorsal Stream (V1, V2, V3, MT, MST, Other dorsal
areas)
– Area MT (temporal lobe)
• Most cells: Direction-selective; Respond more to
the motion of objects than their shape
– Beyond area MT - Three roles of cells in area MST
(parietal lobe)
• Navigation
• Directing eye movements
• Motion perception

• The Ventral Stream (V1, V2, V3, V4, IT, Other ventral
areas)
– Area V4
• Achromatopsia: Clinical syndrome in humans-
caused by damage to area V4; Partial or complete
loss of color vision
– Area IT
• Major output of V4
• Receptive fields respond to a wide variety of colors
and abstract shapes

From Single Neurons to Perception
• Visual perception
– Identifying & assigning meaning to objects
• Hierarchy of complex receptive fields
– Retinal ganglion cells: Center-surround
structure, Sensitive to contrast, and wavelength
of light
– Striate cortex: Orientation selectivity, direction
selectivity, and binocularity
– Extrastriate cortical areas: Selective responsive
to complex shapes; e.g., Faces

From Single Neurons to Perception
• From Photoreceptors to Grandmother Cells
– Grandmother cells: Face-selective neurons in area
IT?
– Probably not: Perception is not based on the activity
of individual, higher order cells
• Parallel Processing and Perception
– Groups of cortical areas contribute to the perception
of color,motion, and identifying object meaning

Concluding Remarks
• Vision
– Perception combines individually identified properties
of visual objects
– Achieved by simultaneous, parallel processing of
several visual pathways
• Parallel processing
– Like the sound produced by an orchestra of visual
areas rather than the end product of an assembly
line

• Cytochrome Oxidase Blobs
– Cytochrome oxidase: mitochondrial
enzyme used for cell metabolism
– Blobs: Cytochrome oxidase staining
in striate cortex
– Each blob centered on an ocular
dominance column in layer IV
– Receive koniocellular inputs from
LGN

Differences in the Sensitivity of M and P Cells to Stimulus
Features

Luminance contrast is a measure of the difference between the brightest and darkest
parts of the stimulus—M cells respond when contrast is as low as 2%, whereas P
cells rarely respond to contrasts less than 10%
Spatial frequency is the number of repetitions of a pattern over a given distance. For
example, alternating light and dark bars each occurring 10 times over a visual angle
of one degree have a spatial frequency of 10 cycles per degree
Temporal frequency is how rapidly the pattern changes over time; turning the bars of
a grating on and off 10 times per second would produce a temporal frequency of 10
Hz. The M cells tend to have lower spatial resolution and higher temporal resolution
than P cells.
The P cells respond to changes in color (red/green and blue/yellow) regardless of
the relative brightness of the colors, whereas M cells respond weakly to changes of
color when the brightness of the color is matched

End of Presentation

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