The Sensorimotor system_Final_noAudio_2021.pdf

Biopsychology Part II Welcome ☺ Today: Sensorimotor Systems General hints • Each lecture is a stand-alone topic Pinel & Barnes, Chapter 8 Week 7: Hunger & Eating • Try to focus on the big picture Pinel & Barnes, Chapter 12 Week 8: Sleeping & Dreaming Pinel & Barnes, Chapter 14 Week 9: Addicti...

Biopsychology Part II Welcome ☺ Today: Sensorimotor Systems General hints • Each lecture is a stand-alone topic Pinel & Barnes, Chapter 8 Week 7: Hunger & Eating • Try to focus on the big picture Pinel & Barnes, Chapter 12 Week 8: Sleeping & Dreaming Pinel & Barnes, Chapter 14 Week 9: Addiction & Reward Pinel & Barnes, Chapter 15 Week 10: Health & Stress Pinel & Barnes, Chapter 17 (last half) • Use “Today’s Goals” as study guides for revision • Learning outcomes from the book chapter The Sensorimotor system The Sensorimotor system (or how does our brain move our body?) Motor control is everywhere – even in a stuffy lecture hall! University of Dundee as a Hierarchical Control System Top-down information flow ABSTRACT Vice Chancellor Dean of Social Sciences Head of Psychology Biopsychology Elaine Niven CONCRETE Blair Saunders Dean of Life Sciences Head of Law Cognition Ben Vincent Anne Keitel Bottom-up information flow Today’s goals Describe and explain the basic principles of hierarchical systems, and their relation to the sensorimotor system Identify the major regions of the sensorimotor cortex and summarise evidence of their function Describe the organisation of the primary motor cortex and its function List and describe the neurons and tracts that connect the brain to skeletal muscles to allow movement Explain the withdrawal reflex, and how this relates to the non-cephalic control of movements Describe sensorimotor programs and their development The Sensorimotor system Blair Saunders Part 1: A sensorimotor hierarchy within the brain General model of Sensorimotor function General model of Sensorimotor function General model of Sensorimotor function General model of Sensorimotor function General model of Sensorimotor function Sensorimotor Association Cortex The top of the sensorimotor hierarchy—so it should be abstract, goaldirected, planning, deliberate intentions Two main areas: • Posterior Parietal Association Cortex • Dorsolateral Prefrontal Association Cortex Posterior Parietal Association Cortex Prior to initiating movements, we need to gather and integrate information. Posterior Parietal Association Cortex (2) What happens when you stimulate the PPC during neurosurgery? Posterior Parietal Association Cortex (2) What happens when you stimulate the PPC during neurosurgery? Low intensity stimulation (5 mA) → strong intention and desire to move contralateral limbs or facial muscles “I felt a desire to lick my lips” High intensity stimulation (8 mA) → illusory experience of actual movement “I moved my mouth, I talked, what did I say?” Desmurget et al. (2009). Science Damage to Posterior Parietal Association Cortex (3) – Apraxia - Usually caused by damage to posterior parietal cortex (e.g., stroke, brain injury, neurodegenerative disease). Term apraxia comes from the Greek a (“without”) and praxis (“action”). Difficulty planning to perform requested voluntary movements “on command” • Deficit in voluntary, “willed” action, rather than a general motor deficit • Textbook example: A carpenter might be able to use a hammer frequently in their day job, but not able to make a “hammering” action on request. • Challenges particularly prevalent when a movement is required out of context, or if the movement itself is imagined rather than real. Posterior Parietal Association Cortex (5) – Contralateral Neglect Posterior parietal damage → disrupted ability to attend to stimuli on one side of the body Typically caused by unilateral damage to cortex Ego-centric bias Items on the opposite side of the body are not attended to by the person. Seems to be a bias in conscious attention Dorsolateral Prefrontal Association Cortex (DLPFC) Receives projections from PPC Inputs to secondary motor cortex, primary motor cortex, and frontal eye fields In monkeys, neurons in the DLPFC tend to fire in anticipation of overt motor responses, and before firing happens in the primary motor cortex DLPFC is a relay brain area? DLPFC might facilitate decisions to make overt actions HOMEWORK EXCERCISE Secondary Motor Cortex Primarily receives input from association cortex and feeds information into the primary motor cortex In the organisation of the motor hierarchy, the secondary motor cortex might be thought of as middle management. Takes general instruction from association cortex and creates more complex movements Secondary Motor Cortex Includes supplementary motor area, premotor area, and cingulate motor area Sends majority of input to primary motor cortex Unlike association cortex, stimulation of secondary motor areas produces physical movements on both sides of the body Recordings from secondary motor cortex show activity both before and throughout overt actions Generally programs complex patterns of movements, after taking instruction from association cortex Secondary Motor Cortex: Mirror Neurons Mirror Neurons and fMRI Primary Motor Cortex Major point of convergence for cortical sensorimotor signals The primary departure point of motor signals from the cerebral cortex Less concerned with abstract planning, and more concerned with sending specific motor commands to the body? The Primary Motor Cortex Neural Cartography! Wilder Penfield Penfield (1940s) pioneering work with epileptic patients and brain stimulation Neural cartography = mapping brain function Electrical stimulation → subjective experiences & movement Temporal lobe stimulation → vivid recall of memory Primary motor cortex stimulation → movements of specific muscles, and sometimes the neighbouring muscles Motor homunculus Motor Homunculus (“little man”): • Somatotopic layout • Contralateral activation of muscles • Scaled to intricacy of movement, rather than size of the corresponding body part Motor Homunculus (or how your brain sees your body) Conventional view of primary cortex function Early studies recorded brain activity from the arm area of the motor cortex while people made arm movements in various directions. Individual neurons responded to the specific direction of hand movements Conventional view: each neuron in the primary motor cortex codes the direction of movement Updated view of primary cortex function Later studies used longer bouts of stimulation and found that primary cortex stimulation produced complex movements, such as eating and drinking behaviours. Updated view: each neuron in the primary motor cortex is loosely related to an individual muscle group, but will also engage actions of coordinated muscles to produce “species typical movements” (e.g., eating, grooming, mating behaviours and so on). Brain areas outside the cerebral cortex that are involved in the control of movement Cerebellum: structure and connectivity • • • Latin for “Little Brain” While small, the cerebellum has > half of the brains neurons. That means the cerebellum has more computational power than both hemispheres of the cerebral cortex! Receives diverse inputs: • Primary and secondary motor cortex • Brain stem motor nuclei • Feedback from somatosensory and vestibular systems. Cerebellum: function One hypothesis: Thought to compare various inputs and correct movements online, as they happen. Cerebellum damage: • Loss of precise control over speed, force, and direction of movement • Difficulty maintaining steady posture, balancing, speech, and eye-movements • BUT, deficits are not exclusively sensorimotor. Cerebellum damage also → cognitive, sensory, and emotional deficits. • Broad deficits make it hard to tie the cerebellum to a particular process In truth, the cerebellum is still quite poorly understood. End of our journey through the sensorimotor hierarchy Neuroprosthetics: Class exercise Neuroprosthetics: Class exercise Where in the cortical hierarchy should we place the electrode? The Sensorimotor system Blair Saunders Part 2: Connecting the brain to the body Connecting the brain to the body Dorsolateral Pathways: Anatomy Ventromedial Pathways: Anatomy Spinal cord basics Descending (efferent) pathways carry motor information to the muscles, ascending (afferent) pathways carry sensory feedback to brain and interneurons The spinal cord itself has some computational complexity Some movements and reflexes can be executed entirely within the spinal cord Motor Neurons, Motor Units, and Muscles Motor neuron = a neuron with its cell body located in spinal cord that projects to organs of movement (e.g., muscles). Motor units = smallest unit of motor activity • 1 motor neuron + the muscle fibers it innervates • Motor neuron firing → simultaneous contraction of connected muscle fibers • Each muscle = Group of muscle fibers held together by a tendon • Each muscle can only contract in one direction Motor pool = All of the motor neurones that innervate a single muscle The relationship between muscles matters Flexors – Extensors Synergistic muscles – Antagonistic muscles Reciprocal Innervation Key principle of spinal cord circuitry Problem: Smooth limb movements would not be possible if two antagonistic muscles were fully active at once Reciprocal innervation means that the activation of one of the antagonistic muscles leads to the inhibition of the other. Think of bending your elbow… you can’t do it if both the biceps and triceps are active Reciprocal Innervation: Withdrawal Reflex Reciprocal innervation ensures that the reflex occurs smoothly. Reflex is carried out quickly by computations conducted by interneurons in the spinal grey matter—no brain required? This is highly adaptive— direct control from the brain would be too slow? Many reflexes are more complex and plastic than withdrawal What route should I take home? Did I lock my office door? What should I eat tonight? Do you need a brain to walk? Grillon (1985) Cat’s spinal cords separated from the brain via transection Cats then held on a sling over a moving treadmill Movement from treadmill generates a sense of sensory feedback that normally occurs during walking. And the cat starts to make walking movements Intriguing suggestion: Walking also appears to be a reflex to stimulation. The movements underlying walking do not rely on hierarchical input from the brain. What does this mean for the hierarchical structure of the sensorimotor system? Central Sensorimotor Programs Most complex processes are a combination of well-established simpler processes performed by the lower-level components of the sensorimotor system. • • • Idea that all but the very highest levels of sensorimotor hierarchy have certain patterns of activity stored into them. Higher level areas contain more abstract motor programs that activate more specific actions in lower areas. Once central sensorimotor programs activated, learned, and stored, lower areas can operate independently, without top-down input What does this mean for the hierarchical structure of the sensorimotor system? Central Sensorimotor Programs Abstract idea “PACK UP AND GO HOME” might be initiated by higher-level brain areas involved in planning and decision making Sensorimotor programmes: Close laptop/notebook Put in bag Stand up and turn to aisle Walk home Sensorimotor programmes and signing you name Movement to create letters + learned grip and movement to control a pen Movement to create letters + learned grip and movement to hold a big stick with two hands The Development of Central Sensorimotor Programs Some sensorimotor programs develop without practice (Fentress, 1973) Typical Mouse grooming behaviour: Coordinated movements of the forelimbs and shoulders, tilt of the head, closing on the eyes, and mouth movements to clean the face. The Development of Central Sensorimotor Programs Other sensorimotor programs develop with practice. “It takes 10,000 hours to become an expert at a given skill” (Malcolm Gladwell). Shifting Control to Lower Levels • This move frees higher level brain structures to deal with more demanding or abstract aspects of performance When you are writing an essay you can think about what to say without thinking about every keystroke • Speed Responses occur faster because responses can be prepared while others are being executed The Development of Central Sensorimotor Programs Comparison of PET activity during newly-learned versus well-practiced tasks Jenkins et al 1994 What does this mean for the hierarchical structure of the sensorimotor system? PARRALLEL PROCESSING Summary The sensorimotor system is organised hierarchically Association cortex tends to be involved in abstract goal intentions, with more concrete execution of movements happening as we descend down the sensorimotor pathways Some sensorimotor activities can be achieved entirely within lower levels of the hierarchy, using central sensorimotor programs Sensorimotor programs can be both innate or learned L5 Conversion Assignment 2 • Two short answer questions from each of the 5 remaining lectures • Focus mainly on describing theories, concepts, and empirical research • Designed to test knowledge and understanding of theory and methods • E.g., • Describe theory x and theory y, and explain why they make different predictions about concept z L5 Conversion Assignment 2 • Each short answer should be approximately 150 words, with a maximum of 200 words per question • Questions will be released at the end of each class, and students should submit each answer by the following Monday in the assessment area of MyDundee. • You can continue to revise your answers until the final deadline Monday 13th December @12 noon. However, we recommend that you submit questions every week so that you have answers in the system • Latest possible submission (if you cannot make the deadline) is Friday the 17th of December @ 12 noon – late submissions apply L5 Conversion Assignment 2 (example question 1) • Describe theory x and theory y, and explain why they make different predictions about concept z • Answers need to be concise in order to cover the breadth of the question • E.g., ~50 words on each definition, and 50 words comparing the key predictions for the phenomena of interest. L5 Conversion Assignment 2 (example question 2) • What is the function of brain region x, and select ONE piece of evidence that supports the functional role of this brain region. • Answers need to be concise in order to cover the breadth of the question • E.g., ~50 words to describe the region, and 100 to describe how and why a key piece of research supports the functional role of the region. This week’s questions • 1. Why is the posterior parietal cortex identified as an area of association cortex, and what is this region’s role in the sensorimotor hierarchy? • 2. Define the theory of central sensorimotor programs and describe ONE piece of evidence supporting their development EITHER with or without practice.