Occipital lobe

Where is the occipital lobe?

It rests on the tentorium cerebelli, which lies in the transverse fissure between the cerebral hemisphere and the cerebellum. (Neuroscience Online, Overview of the Nervous System)

On the medial surface, the parieto-occipital sulcus marks it off from the parietal lobe. The lateral surface has no such groove, so anatomists draw the border as an imaginary line from the tip of that sulcus to the preoccipital notch. (OpenStax A&P 2e, 13.2; Neuroscience Online, Overview of the Nervous System)

What are the parts of the occipital lobe?

On the medial surface, the calcarine fissure and the parieto-occipital sulcus define the cuneus, with the lingual gyrus below it. (Neuroscience Online, Overview of the Nervous System)

The primary visual cortex, Brodmann’s area 17, is the striate cortex. It straddles the calcarine fissure and wraps around the occipital pole onto the lateral side of the lobe. (Neuroscience Online, Visual Processing: Cortical Pathways; OpenStax A&P 2e, 16.2)

What does the occipital lobe do?

Areas 18 and 19, the extrastriate cortex around the primary visual cortex, carry out later stages of visual processing. (OpenStax A&P 2e, 16.2; Neuroscience Online, Visual Processing: Cortical Pathways)

In the primary visual cortex, most cells outside the color-sensitive blobs respond to either eye, and many fire best for an edge at one orientation. These cells start the analysis of shape. (OpenStax A&P 2e, 14.2; Neuroscience Online, Visual Processing: Cortical Pathways)

Each side’s visual cortex handles the opposite half of the visual field, and the map is upside down: the upper bank of the striate cortex receives the lower half of the field, and the lower bank the upper half. (OpenStax A&P 2e, 14.2; StatPearls, Visual Cortex; Neuroscience Online, Visual Processing: Cortical Pathways)

Where does visual information come from and go next?

The visual relay in the thalamus is the lateral geniculate nucleus, whose axons project to the visual cortex in the occipital lobe. (Neuroscience Online, Visual Processing: Cortical Pathways; OpenStax A&P 2e, 14.2)

The extrastriate cortex surrounds V1 in the occipital lobe, and its two main areas next to V1 are V2 and V3. StatPearls divides the visual cortex into five areas, V1 to V5, and V1 sends its color, shape, location and motion signals to separate parts of the extrastriate cortex. (OpenStax A&P 2e, 14.2; Neuroscience Online, Visual Processing: Cortical Pathways; StatPearls, Visual Cortex)

From there, processing splits in two. A ventral stream to the inferior temporal cortex identifies objects and colors, and a dorsal stream to the parietal cortex tracks where things are and guides your movements toward them. (OpenStax A&P 2e, 14.2; Neuroscience Online, Visual Processing: Cortical Pathways; Goodale and Milner 1992, Trends Neurosci)

Where the sources differ

Sources differ on which Brodmann areas make up the primary visual cortex. OpenStax A&P 2e section 13.2 says areas 17 and 18 are responsible for primary visual perception. Section 16.2 and Neuroscience Online give area 17 alone, with areas 18 and 19 as later stages. (OpenStax A&P 2e, 13.2 and 16.2; Neuroscience Online, Visual Processing: Cortical Pathways)