OCCIPITAL LOBES
Location
The occipital lobes form the posterior pole of the cerebral hemispheres
Lies beneath the occipital bone at the back of the skull
On the medial surface of each hemisphere, the occipital lobe is distinguished from the parietal
lobe by the parietal-occipital sulcus
No clear landmarks separate the occipital cortex from the temporal or parietal cortex on the
lateral surface of the hemisphere because the occipital tissue merges with the other regions
This makes it difficult to define the extent of the occipital areas precisely
Within the visual cortex are three clear landmarks:
The most prominent is the calcarine sulcus → which contains much of the primary cortex
→ divides the upper and lower halves of
the
visual world
On the ventral surface of each hemisphere are two gyri
• Lingual → contains part of visual cortical areas V2 and VP
• Fusiform → contains V4
Anatomy: Subdivisions and Connections
The occipital cortex is subdivided into different visual areas:
• V1, V2, V3, VP, V3a, V4d, V4v, DP, MT (V5)
Some of the areas contain a complete visual field, whereas others have only an upper or lower
visual field.
The V1 area, nicknamed the “straite cortex” due to its complex laminar organization: cortical
layer IV, features four distinct layers and appears as a thick stripe
The visual cortex contains distributed hierarchical processes with multiple parallel and
interconnecting pathways at each level
V1 (the striate cortex) is the primary vision area: it receives the largest input from the lateral
geniculate nucleus of the thalamus, and it projects to all other occipital regions. VI is the first
processing level in the hierarchy.
V2 also projects to all other occipital regions. V2 is the second level.
After V2, three distinct, parallel pathways emerge enroute to the parietal cortex, superior
temporal sulcus (STS), and inferior temporal cortex, for further processing
Three parallel pathways (streams) develop from here:
• Dorsal stream → parietal lobe - visual guidance of movement [WHERE]
• Ventral stream → inferior temporal lobe – object perception, colour [WHAT]
• Middle pathway STS stream → superior temporal sulcus – perhaps visuospatial
functions
At each level in the visual system, there is a clear spatial mapping of the visual world. It is
possible to identify cells at each level that respond to stimuli at a certain point in space these
cells are arranged in a way that corresponds to the relationships of the points in external
space, although with some minor distortions.
Function: The Occipital Lobes house vison!
Area V1 is primary for vision and must function must function so that the brain can make sense
of the more specialised visual areas of processing
