visual cortex

Examples of visual cortex in the following topics:

• Visual Processing

  • Visual signals are processed in the brain through several different pathways.
  • Within the nerves, different axons carry different parts of the visual signal.
  • Once in the brain, visual information is processed in several places.
  • When visual signals leave the thalamus, they travel to the primary visual cortex at the rear of the brain.
  • From the visual cortex, the visual signals travel in two directions.

• Cerebral Hemispheres and Lobes of the Brain

  • The left temporal lobe holds the primary auditory cortex, which is important for processing the semantics of speech.
  • The occipital lobe contains most of the visual cortex and is the visual processing center of the brain.
  • The visual cortex receives raw sensory information through sensors in the retina of the eyes, which is then conveyed through the optic tracts to the visual cortex.
  • Damage to the primary visual cortex (located on the surface of the posterior occipital lobe) can cause blindness, due to the holes in the visual map on the surface of the cortex caused by the lesions.
  • The parietal lobe is comprised of the somatosensory cortex and part of the visual system.

• Sensory Areas

  • Most sensory information is routed to the cerebral cortex via the thalamus.
  • The visual area is located on the calcarine sulcus deep within the inside folds of the occipital lobe.
  • For example, the right primary somatosensory cortex receives information from the left limbs, and the right visual cortex receives information from the left eye.
  • Neighboring points in the primary visual cortex, for example, correspond to neighboring points in the retina.
  • Similarly, there is a tonotopic map in the primary auditory cortex and a somatotopic map in the primary sensory cortex.

• Perceiving Depth, Distance, and Size

  • Visual stimuli enter as light through the photoreceptors in the retina, where they are changed into neural impulses.
  • These impulses travel through the central nervous system, stop at the sensory way-station of the thalamus, and then are routed to the visual cortex.
  • From the visual cortex, the information goes to the parietal lobe and the temporal lobe.
  • Approximately one-third of the cerebral cortex plays a role in processing visual stimuli.
  • Convergence upon a single point is another visual cue that provides information about distance.

• Thalamus

  • Its functions include relaying sensory and motor signals to the cerebral cortex and regulating consciousness, sleep, and alertness.
  • It is generally believed to act as a relay between a variety of subcortical areas and the cerebral cortex.
  • For the visual system, for example, inputs from the retina are sent to the lateral geniculate nucleus of the thalamus, which in turn projects to the primary visual cortex in the occipital lobe.
  • Each of the primary sensory relay areas receives strong back projections from the cerebral cortex.
  • The ventral posterior nucleus is a key somatosensory relay, which sends touch and proprioceptive information to the primary somatosensory cortex.

• Cerebral Lobes

  • The cortex is divided into four main lobes: frontal, parietal, occipital, temporal.
  • For example, it comprises the somatosensory cortex and the dorsal stream of the visual system.
  • This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions.
  • The areas associated with vision in the temporal lobe interpret the meaning of visual stimuli and establish object recognition.
  • Anterior parts of this ventral stream for visual processing are involved in object perception and recognition.

• Parts of the Cerebellum

  • The surface of the cerebellum is covered with finely spaced parallel grooves, in striking contrast to the broad irregular convolutions of the cerebral cortex.
  • Like the cerebral cortex, the cerebellum is divided into two hemispheres.
  • Its primary connections are with the vestibular nuclei, although it also receives visual and other sensory input.
  • It receives proprioception input from the dorsal columns of the spinal cord (including the spinocerebellar tract) and from the trigeminal nerve, as well as from visual and auditory systems.
  • It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming corticopontocerebellar pathways), and sends output mainly to the ventrolateral thalamus (in turn connected to motor areas of the premotor cortex and primary motor area of the cerebral cortex) and to the red nucleus.

• Overview of the Cerebrum

  • It is primarily involved in vision: seeing, recognizing, and identifying the visual world.
  • Damage to motor areas of cortex can lead to certain types of motor neuron disease.
  • Speech and language are mainly attributed to parts of the cerebral cortex.
  • The cerebral cortex is the outer layer depicted in dark violet.
  • Notice the folded structure of the cortex: the "valleys" of the cortex are known as sulci.

• Brain: Cerebral Cortex and Brain Lobes

  • For example, when an object is presented to patients' left visual fields, they may be unable to verbally name the object (and may claim not to have seen an object at all).
  • This is because the visual input from the left visual field crosses and enters the right hemisphere and is unable to signal to the speech center, which generally is found in the left side of the brain.
  • The parietal lobe contains a somatosensory map of the body similar to the motor cortex.
  • It is primarily involved in vision: seeing, recognizing, and identifying the visual world.
  • Different parts of the motor cortex control different muscle groups.

• Mapping the Primary Somatosensory Area

  • It is a visual representation of the concept of the body within the brain—that one's hand or face exists as much as a series of nerve structures or a neuron concept as it does in a physical form.
  • Each one shows a representation of how much of its respective cortex innervates certain body parts.
  • The primary somesthetic cortex (sensory) pertains to the signals within the postcentral gyrus coming from the thalamus, and the primary motor cortex pertains to signals within the precentral gyrus coming from the premotor area of the frontal lobes.
  • Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus).
  • Areas such as the appendages, digits, and face can draw their sensory locations upon the somatosensory cortex.