Dorsal stream

From neurov.is/on

The dorsal stream (green) and ventral stream (purple) are shown. They originate from primary visual cortex.

The dorsal stream is proposed to be involved in the guidance of actions and recognizing where objects are in space. Also known as the parietal stream, the "where" stream, or the "how" stream, this pathway stretches from the primary visual cortex (V1) in the occipital lobe forward into the parietal lobe. It is interconnected with the parallel ventral stream (the "what" stream) which runs downward from V1 into the temporal lobe.

[edit] General features

The dorsal stream is involved in spatial awareness and guidance of actions (e.g., reaching). In this it has two distinct functional characteristics - it contains a detailed map of the visual field, and is also good at detecting and analyzing movements.

The dorsal stream commences with purely visual functions in the occipital lobe before gradually transferring to spatial awareness at its termination in the parietal lobe.

The posterior parietal cortex is essential for, "the perception and interpretation of spatial relationships, accurate body image, and the learning of tasks involving coordination of the body in space"^[1]

It contains individually functioning lobules, one area of which contains neurons that produce enhanced activation when attention is moved onto the stimulus or the animal saccades towards to a visual stimulus (LIP), and another section where visual and somatosensory information are integrated (VIP).

Dorsal - Ventral Stream

[edit] Effects of damage or lesions

Damage to the posterior parietal cortex causes a number of spatial disorders including:

• Simultanagnosia: where the patient can onl.y describe single objects without the ability to perceive it as a component of a set of details or objects in a context (as in a scenerio, e.g. the forest for the trees).
• Optic ataxia: where the patient can't use visuospatial information to guide arm movements.
• Hemispatial neglect: where the patient is unaware of the contralesional half of space (that is, they are unaware of things in their left field of view and focus only on objects in the right field of view; or appear unaware of things in one field of view when they perceive them in the other). For example, a person with this disorder may draw a clock, and then label it from 12, 1, 2, ..., 6, but then stop and consider their drawing complete.
• Akinetopsia: inability to perceive motion.
• Apraxia: inability to do discretionary or volitional movement in the absence of muscular disorders.