Week 4 PDF: Brain Function

THE BRAIN ~2% of body weight; receives ~20% of blood pumped from the heart consumes ~20% of body’s energy 100 billion neurons 1,000,000 billion synapses (connections between neurons...

THE BRAIN ~2% of body weight; receives ~20% of blood pumped from the heart consumes ~20% of body’s energy 100 billion neurons 1,000,000 billion synapses (connections between neurons) 101,000,000 possible circuits Cerebrum Cerebral Hemispheres Forebrain Cerebellum Hind brain Brainstem 2  Longitudinal Fissure Cerebrum (inter-hemispheric fissure) (Cerebral Hemispheres) Two Hemispheres, divided by Longitudinal Fissure or Inter-Hemispheric Fissure 3 Intelligence: Size is not everything Apart from size, what is different?  Cerebral Cortex The outermost surface layer of the cerebrum = Grey matter Cerebral Cortex 5 Cortex = Grey Matter Surface of the brain 2 to 4 mm thick Contains the cell bodies of the brain’s neurons Highly folded to maximize surface area. i.e. maximize amount of cortex that can fit inside skull White matter underneath the grey matter is all the “wiring” i.e. axons of the neurons, connecting to the spinal cord and to other areas of the cortex 6 1 2 Frontal Lobe Executive Functions: – reasoning, planning, problem-solving – Inhibitory control – Working memory Motor functions – Premotor cortex – motor planning – Primary motor cortex – execution Speech production (Broca’s area) 3 Parietal Lobe Primary Somatosensory Cortex – Perception of touch Sense of space and locations – Gives sense of stable world around us relative to our body position Spatial attention – Directing attention and eye-movements to explore visual world Linking vision to action – Represents spatial location of objects around us for guiding actions 4 Occipital Lobe Posterior part of the brain, inferior to Parietal Lobe Primary Visual Cortex (V1) – All visual perception Higher visual areas – Different regions process shape, colour, orientation, motion 5 Temporal Lobe Primary Auditory Cortex – Perception of sound Language Comprehension (Wernicke’s area) Medial Temporal Lobe: – Limbic system amygdala and hippocampus 6  Limbic System Medial Temporal Lobe Amygdala Fear and arousal – Responds to threat / danger (snakes, spiders, angry/fearful faces) – Fear / learning Phobias? Hippocampus Learning and Memory – Forming new episodic memories – Damage causes anterograde amnesia (can’t form new memories of events) Amygdala = Almond Hippocampus = Seahorse 7 Corpus Callosum Neuron connections between the left and right hemispheres Allows brain communication between hemispheres “Split-Brain” patients – left and right hemispheres disconnected. The two hemispheres cannot communicate with each other. 8 9 1  Brain Function (1957) Before MRI 2 Phineas Gage Railway worker, Phineas Gage, accident in 1848 Iron rod, about 1m length, went through his head Remained conscious during and after accident Damaged frontal lobes Died 12 years later and his skull was examined 3  Phineas Gage Gage’s physician John Harlow reported profound change in personality “The equilibrium or balance, so to speak, between his intellectual faculties and animal propensities, seems to have been destroyed. He is fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom) … impatient of restraint or advice when it conflicts with his desires …” Changed into a man who was “no longer Gage” Important role of frontal lobe for executive control of behaviour 4  Broca’s Area – Speech Production In 1861, Paul Broca described a patient who was unable to speak after damage to the left frontal lobe (Broca’s area) 5 Broca’s Aphasia – Speech Production Speech is slow and non-fluent Difficulty finding appropriate words (anomia) Speech still carries meaning Comprehension is (mostly) unaffected 6 Wernicke’s Area – Language Comprehension In 1874, Carl Wernicke suggested that lesions to the left posterior temporal lobe led to deficits in language comprehension. 7 Wernicke’s Aphasia – Comprehension Unable to understand language – deficit in comprehension Speech is fluent with normal prosody (rhythm, intonation) Speech has no meaning, nonsense speech 8  Left Hemisphere Broca’s and Wernicke’s area Speech production Language comprehension 9  Wilder Penfield Stimulated the brain with electrical probes while the patients were conscious, during surgery for epilepsy. 1951, published maps of motor and sensory cortices of the human brain 10  “Homunculus” Sensory Motor Primary Sensory cortex and Primary Motor cortex Brain function “mapped” by electrical stimulation Brain stimulation leads to sensation or movement (muscle twitch) Size of area on cortex determines sensitivity or fine motor control 11  Brain Function (1957) Before MRI 12 The Brainstem 1 Autonomic Nervous System Central Nervous System Brain and spinal cord Peripheral Nervous System Somatic Nervous System – Voluntary – Motor and Sensory Autonomic Nervous System – Involuntary – Heart-rate, respiration, sweating – Stress, arousal, “fight-or-flight” 2  Autonomic Nervous System 2 divisions: Sympathetic Nervous System – Emotional arousal, stress, fear – “Fight or Flight” response – Increases heart-rate, respiration, perspiration, pupils dilate. Parasympathetic Nervous System – “Rest and digest” – Lowers heart-rate, respiration – Increases stomach, intestine activity (digestion) – “opposes” the sympathetic nervous system 3 Brainstem Medulla Autonomic nervous system functions Controls heart-rate, respiration, regulation of blood pressure, body temperature Reflex centres for coughing, sneezing, swallowing, vomiting 4 Disorders of Consciousness Persistent Vegetative State Severe damage to upper brain (hemispheres and cortex) If brainstem is not damaged, autonomic nervous system functions can remain sometimes normal respiration, control of heart rate, some face and eye movements remain Patients have no conscious awareness 5 6 Disorders of Consciousness “Locked-in” Syndrome Amyotrophic Lateral Sclerosis (ALS) or Motor Neuron disease – Loss of motor neurons to spinal cord or Brain injury (following accident) Intact cerebrum and brainstem, but “disconnected” from spinal cord Normal cognitive function, vision, and hearing, but patients cannot move Patients may be fully conscious and aware, but totally unresponsive 7  Disorders of Consciousness “Locked-in” patients appear the same as those with persistent vegetative state Cortex is fully functioning What is their conscious awareness? Functional MRI to detect brain activity and allow some communication “Imagine playing tennis” “Imagine walking around your house” https://www.youtube.com/watch?v=UGYF2xOt-zk 8 Low-level to High-level function High Level Cerebral Hemispheres – Cortex Planning, reasoning, problem-solving (frontal lobe) Language and Perception Brainstem Autonomic nervous system functions (heart-rate, respiration, blood pressure) Low Level 9 Cerebellum and Motor Cortex 1 Cerebellum Hind brain (latin for little brain) Sense of balance and co-ordination of complex movement Motor learning – fine adjustment of movement based on feedback 2 Primary Motor and Sensory Areas “Homunculus” Primary motor cortex activity leads to movement (muscle contraction) Primary sensory cortex activity leads to sensation Different parts of motor and sensory cortex map to different parts of the body (homunculus) 3  “Motor Programs” for movement Movements planned and “programmed” in the brain before initiation, like a computer program (theory from 1960’s) Brain creates program just before movement. OR Brain retrieves program for learnt skilled actions – eg signature, tennis swing, etc Motor Cortex (causes movement) Muscles to move (motor program) 4  Feedback control of Movement Planned actions compared with feedback from actual actions performed Does it match? Rapidly correct action, Learn for future Brain computes difference between planned action and Vision feedback during performed action Sensation (hands on racquet) Proprioception (body position) 5  Did I do that? Sense of Agency When feedback matches predictions from planned actions Brain automatically links sensory events and own- actions to infer causality Sense that my action caused that event Can’t tickle yourself !! The tickle machine Only “tickles” when sensory stimulus does not match own-action Blakemore et al., 1998, 6 Nature Neuroscience 7