Lecture 11 - ‘Higher’ cortical function Flashcards
describe the cerebral cortex
- Thin layer of grey matter
- Sitting on the superficial surface of the cerebral hemispheres
- 5-6mm thick
- Arranged in 6 cortical layers
complex functions of the cerebral cortex
- Behaviours
- Thoughts
- Emotions
Majority of inputs to the cortex:
- From the thalamus
- From other parts of the cortex
- Recurrent feedback loops where cortex provides its own input – e.g. one thought leading to another
- Monamine neurones
Majority of outputs from the cortex:
- Other cortical regions
- Pyramidal cells
- Large neurones which send structures down to the:
- basal ganglia
- caudate putamen and pons
- reticular formation and red nuclues
- spinal cord, brainstem and cranial nerves
- basal ganglia
- Large neurones which send structures down to the:
Cortex is not homogenous
*
- Phrenologists believed that personality traits and tendencies to crime etc could be correlated with the size of bony prominence’s on the skull
- Now discounted but early inspiration for cortical localisation
Cortical localisation
- Various regions of the cortex have different functional properties
- Demonstrated by strokes
- Different histological regions of the cortex
Different functional regions of the cortex
Frontal
Parietal
Temporal
occipital
location of the frontal lobe
anteriro to central sulcus
Major functions of the frontal lobe
- Motor
- Primary motor cortex
- Motor homunculus
- Expression of speech (usually left hemisphere)
- Behavioural regulation/judgement
- Cognition
- E.g. mathematical ability
- Eye movement
- Region called frontal eye field
- Projects down onto the brainstem and communicates with CN nuclei relevant to the eyes
- Continence
- Paracentral lobule (near midline)- regulates micturition
example of Behavioural regulation/judgement role of the frontal lobe
E.g. Phineas Gage story- iron rod went through frontal lobe. Became impulsive, alcoholic and violent behaviour significantly changed
location of the parietal lobe
Posterior to central sulcus
major functions of the parietal lobe
- Sensory
- Comprehension of speech (usually left hemisphere)
- Wernicke’s area
- Body image (usually right)
- Awareness of external environment (attention)
- Condition called Neglect – despite the fact pt has normal visual field, they can’t acknowledge the existent of one of half of their environment
- Calculation and writing
- Don’t forget visual pathways projecting through white matter
- Superior optic radiations pass through the parietal lobe
what condition regarding awareness of external enbironemnt can occur if the parietal lobe is damaged
Neglect
hemispatial neglect
Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain is sustained, a deficit in attention to and awareness of one side of the field of vision is observed. It is defined by the inability of a person to process and perceive stimuli on one side of the body or environment, where that inability is not due to a lack of sensation.[1] Hemispatial neglect is very commonly contralateral to the damaged hemisphere, but instances of ipsilesional neglect (on the same side as the lesion) have been reported.
ie.
- despite the fact pt has normal visual field, they can’t acknowledge the existent of one of half of their environment
which side of the brain is most responsible for comprehension of speech
left hemisphere in the wernickes area (parietal)
temporal lobe located
inferior to synvian fissure
major functions of the temporal lobe
- Sensory (relatively posterior)
- Hearing- primary auditory cortex (superior)
- Olfaction- primary olfactory cortex (inferior)
- Memory
- Hippocampus sits deep in the temporal love e.g. factual memory
- Emotion
- Thought olfactory centre (smell)is linked to emotional function
- Don’t forget visual pathways projecting through white matter
- Inferior optic radiations pass through the temporal lobe
location of the occpital lobe
posterior to the parietal and temporal lobes. Thus, it forms the caudal part of the brain
major function of the occipital lobe
visual processing area of the brain. It is associated with visuospatial processing, distance and depth perception, color determination, object and face recognition, and memory formation
cerebral dominance/lateralisation
Asymmetry in the functions of the left and right cerebral hemispheres
- Left hemisphere is dominant in 95% of people (think about how it controls the right hand)
- Right hemispheres attends to both halves of spaces but the left hemispheres only attends only to the right half of space
- This links to Neglect disorder
Left hemisphere
Sequential processing (processing which occurs in a serial fashion):
- Language
- Mathematic/logic
Right hemisphere
Whole picture processing:
- Body image
- Visuospatial awareness
- Emotion
- Music
the corpus callosum
Allows the left and right hemispheres to work together
A huge bundle of white matter connecting the two hemispheres. An early surgical treatment for severe epilepsy was to cut the corpus callosum to prevent seizure activity from propagating through the whole brain. This had some interesting neuropsychological consequences for those patients…
language pathways are primarily dominant in the
left hemisphere
important ares for correct processing of language
Brocas and Wernickes
For most people, these areas are functional for language primarily in the left hemisphere.
Broca’s area
- Inferior lateral portion (think face of homunculus) of frontal lobe
- Production of speech (motor function)
- Directs muscles to produce language
Wernicke’s area
- Superior portion of temporal (some say parietal as well) lobe
- Near primary auditory region
- Interpretation of language (sensory)
- Understanding of what is being said
Brocas and Wernickes area are connected via
Arcuate fasciculus (green) - white matter pathway
- Best though of as a unidirectional pathway (although is technically bilateral)
1) Pathway for repeating a heard word
- Word heard
- Auditory info is processed in the cortex within the primary auditory cortex and then goes to Wernicke’s area- where it is interpreted and translated into language
- Wernicke’s area then communicates with Broca’s’ area through the arcuate fasciculus
- Broca’s area tells the cortex to produce pattern of muscle contractions which will produce the sound of the word that was previously heard
- Impulse to primary motor cortex (PMC) area which drives the facial and laryngeal muscles, resulting in repetition of heard word
2) Pathway for speaking a written word
- When we read we use primary visual cortex in occipital lobe
- Visual pattern sent from visual cortex to Wernicke’s area
- Wernicke’s is then able to examine pattern as impulses and interpret pattern as a word
- Wernicke’s then sends word via the arcuate fasciculus to Broca’s area
- Broca’s area then instructs PMC to produce a pattern of muscular contraction in order to produce pattern of musculature contraction to produce the read word
3) Pathway for speaking a thought
- Thoughts can arise from many brain regions, but converges at Wernicke’s area
- Wernicke’s interprets thought patterns and converts into language
- Sends impulses to Broca’s via the arcuate fasciculus
- Broca’s sends to PMC instructing to produce pattern of musculature contraction to be able to speak thought
Damage specially to arcuate fasciculus results in patients not being able to
repeat the word
read allowed a word
speak a thought
Wernicke’s aphasia (fluent aphasia)
A type of aphasia (language disorder after stroke) with poor comprehension. Speech is effortless, but the meaning is impaired.
- Speech is very fluent and confident
- Intact Broca’s
- However what they say doesn’t make any sense at all
- Cant understand questions being asked
Broca’s aphasi
A type of aphasia characterized by partial loss of the ability to produce language (spoken, manual, or written), although comprehension generally remains intact
- No problem with understanding questions being asked
- Wernicke’s area intact
- Frustration with trying to articulate answer
- Hesitant and lots of pausing
Types of memory
- Declarative
- Nondeclarative
- Stored in a different regions in the brain therefore differentially effected in different types of brain damage
Declarative memory
- Explicit
- Facts e.g. revising for an exam
Nondeclarative memory
- Implicit
- Motor skills
- Emotions
where are declarative memories stored
Hippocampus which sits in the temporal lobe of thecerebral cortex
the hippocampus
- Called hippocampus due to its resemblance to a seahorse
- Site of association receiving input from multiple regions of the brain
- Visual
- Auditory
- Limbic (emotions)
- Somatosensory
- Through a reverberatory circuit between itself and the cerebral cortex, it is able to produce long term potentiation within the synapses of the cortex in order for us to lay down long term memories
where are non declarative memories stored
in the cerebellum and basal ganglia
How are memories stored?
- Short term memory (seconds to minutes)
- Consolidation of STM to LTM depends on
- Emotional cortex
- Rehearsal
- Association
- Long term memory (up to a lifetime)
Neuroplasticity: molecular and cellular mechanisms of memory
Long term potentiation
- Presynaptic neurone grows more terminals which impinge on post synaptic neurone
- Terminals will release more NT per given stimulus
- More NTs receptors expressed within synapse
