Localisation Of Function

• This is the theory that different areas of the brain are responsible for different behaviours, cognitive processes or activities and are associated with different parts of the body. This is sometimes called cortical specialisation
• Functions in the brain

  • Some functions are more localised than others
  • Motor (movement) functions are highly localised to a particular area of the cortex (motor cortex)
  • Language system functions seem to be more widely distributed, although some components may be localised (e.g. speech comprehension or production)
• If a certain area of the brain is damaged


  The function associated with that area will also be affected
• Holistic theory of the brain

  All parts of the brain are involved in the processing of thought and action
• Before the localisation theory, scientists generally supported the holistic theory of the brain
• •The brain is divided into two symmetrical halves called hemispheres (left and right).•Some functions are dominated by one hemisphere. This is called lateralisation (more to come on this next lesson).•Activity on the left side of body is controlled by the right hemisphere and vice versa.•The outer layer of both hemispheres is called the cerebral cortex. Each hemisphere of the cerebral cortex is made up of four sections called lobes. Within each lobe there are distinct areas that are thought to have different specific functions (localisation).
• l


  l

  
• Somatosensory cortex


  Region of the brain that processes input from sensory receptors in the body that are sensitive to touch
• Somatosensory cortex

  • Located in the parietal lobe, along a region known as the postcentral gyrus
  • Just behind the central sulcus which divides the frontal and parietal lobes
• Sensory information processed by somatosensory cortex

  Touch, pressure, pain and temperature
• Somatosensory cortex

  Localises sensations to specific body regions
• Primary visual centre in the brain

  Located in the visual cortex, in the occipital lobe of the brain
• Both hemispheres have a somatosensory cortex, with the cortex on one side of the brain receiving and processing sensory information from the opposite side of the body
• Visual cortex

  Receives and processes visual information
• Homunculus

  Representation of the amount of somatosensory area devoted to a particular body part, denoting its sensitivity
• Visual processing

  1. Begins in the retina

  2. Light enters and strikes photoreceptors (rods and cones)

  3. Action potentials from the retina transmitted to the brain via the optic nerve

  4. Most action potentials terminate in the thalamus

  5. Thalamus passes information on to the visual cortex
• Receptors for the face and hands occupy over half of the somatosensory cortex and so are very sensitive
• Visual cortex

  • Spans both hemispheres
  • Right hemisphere receives input from left hand side of visual field
  • Left hemisphere receives input from right hand side of visual field
  • Contains several different areas processing different types of visual information (colour, shape, movement)
• •The auditory centre in the brain is concerned with the analysis of speech-based information i.e. hearing. Most of this area lies within the temporal lobes on both sides of the brain, where we find the auditory cortex.•The auditory pathways begin in the cochlea in the inner ear, where sound waves are converted to action potentials, which travel via the auditory nerve to the auditory cortex in the brain. Damage may produce partial hearing loss; the more extensive the damage, the more extensive the loss.
• Systematic research from Wernicke and Broca onwards

  • Demonstrated that in most people language centres are lateralised to the left hemisphere
• Broca's area

  Named after Paul Broca who treated a patient known as 'Tan' because that was the only syllable he could express
• Tan had been able to understand spoken language, but was unable to speak, nor express his thoughts in writing
• Broca then studied other patients who had similar language deficits, along with lesions in their left frontal hemisphere
• Patients with damage to these areas in the right hemisphere did not have the same language problems
• Language centre

  Identified by Broca in the posterior portion of the frontal lobe of the left hemisphere
• Broca's area


  Believed to be critical for speech production
• People with damage to Broca's area (called Broca's aphasia)


  • Often only able to talk in short meaningful sentences which take great effort (they are slow and laborious)
  • Speech lacks fluency as there is a difficulty with words that help sentences to function (e.g. 'it', 'the' etc.)
• Wernicke's area

  An area of the brain involved in understanding language (i.e. the interpretation of speech), located in the posterior portion of the left temporal lobe (encircling the auditory cortex)
• Wernicke's aphasia


  Patients with a lesion in Wernicke's area can speak but are unable to understand language, such that the speech they produce is fluent but meaningless, often producing nonsense words (called neologisms)
• Broca's area

  The motor region of the brain for language, located close to the area that controls the mouth, tongue and vocal cords
• Language processing

  1. Sensory input from auditory and visual regions is transferred to Wernicke's area where it is recognised as language and associated with meaning

  2. Motor output from Broca's area controls the mouth, tongue and vocal cords to produce speech
• Wernicke's area and Broca's area

  There is a neural loop running between them
• Systematic research from Wernicke and Broca onwards has demonstrated that in most people language centres are lateralised to the left hemisphere
• Carl Wernicke discovered Wernicke's area
• •Aphasia refers to an inability (or impaired ability) to understand or produce speech as a result of brain damage.