Transcript brain
The Brain and Behavior Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses: What does the signal do? Reflexes: A model Brain Organizing Principles and Functions Functions • • • • • Communication Coordination Control Cognition Complexity Outline: Start With A Mechanistic View • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses: What does the signal do? Reflexes: A model Brain Organizing Principles and Functions Evolution • • • • None Nerve net Segmented Cephalization: an organizing principle (brainmind correlation not always obvious!) • Kineses • Taxes • Reflexes Evolution Brain Structure Brain Structure Brain Structure DRUGS Evolution • • • • • • • None Nerve net Segmented Cephalization: organizing principle + brain-function rel. Kineses Taxes Reflexes Reflexes • Kinesis (potato bug) • Taxis (moth / maggot / fly / tick) • Reflex: (knee jerk) – Descartes 161 St. Germaine on the Seine – Pineal – Mechanist Reflexes • Braightenberg: Vehicles Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses Reflexes: A model Brain Organizing Principles and Functions The Neuron • 100 billion • Varied in size, shape, function • Function of neuron sending signals in real time (ex.) • What is the signal? - electrical / chemical Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses Reflexes: A model Brain Organizing Principles and Functions Origin of nerve signal • Function of neuron sending signals in real time (ex.) • What is the signal? - electrical / chemical Generation • Two forces: – Electrical (ionic) – Chemical (concentration) – Give rise to steady-state voltage “resting potential” – Universal in cells Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses Reflexes: A model Brain Organizing Principles and Functions Action Potential Movement of a Signal Action Potential • Cell actions • Speed: Muller (light), Helmholtz (43 m/sec) • Refractoriness • All or none law • Coding of intensity: analog-digital + recruitment (organizing principle) Neuron Communication • Propagation is much faster if the axon is myelinated: • Depolarization proceeds down the axon by a number of skips or jumps. • The action potential obeys the all-ornone law: • Once it’s launched, further increases in stimulus intensity have no effect on its magnitude. Neuron Communication • Propagation is much faster if the axon is myelinated: • Depolarization proceeds down the axon by a number of skips or jumps. • The action potential obeys the all-ornone law: • Once it’s launched, further increases in stimulus intensity have no effect on its magnitude. • Frequency signals intensity Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses Reflexes: A model Brain Organizing Principles and Functions Synapses: What happens when signal reaches end of neuron? • Two types of actions - excitatory / inhibitory • Chemical model with multiple & functionally different neurotransmitters • Temporal & spatial summation Synapses Release of Neurotransmitter Synapses Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses Reflexes: A model Brain Organizing Principles and Functions A Model for building behavior out of simple building blocks • • • • Reflexes Voting behavior Mirror neurons Other examples to follow Reflexes: A model Outline • • • • • • • • Functions Evolution: structure and behavior Basic Unit: The Neuron Generation: How does a signal get started? Action Potential: How does a signal move? Synapses Reflexes: A model Brain Organizing Principles and Functions Brain Structure (midline) Structure: Central Core Structure: X-Ray View Methods for studying the brain • Single-cell and population recordings – Animal studies – Surgical patient studies • Stimulation – Animal studies – Surgical patient studies • Damage – Animal lesions – Human injury – Human surgical lesions • Neuroimaging • Electroencephalogram (EEG) recording – Electrodes are placed on the surface of the scalp and record/amplify the electrical signal given off by the brain – Event Related Potentials (ERPs) are used to study how the brain responds to different stimuli or events CT scan MRI scan Functional Magnetic Resonance Imagingin (fMRI) – Measures changes in blood-oxygenlevel-dependent (BOLD) activation – Areas of the brain that are engaged more in a task, require oxygen rich blood – Result show a very small but highly significant percent change in BOLD activation (the entire brain is active all the time) Connectivity measures Functional connectivity – uses resting-state fMRI data to chart cortical regions with temporal synchrony (correlation of activation patterns) Structural connectivity – measures the movement of water molecules to chart the white matter tracts (visualizing anatomy) Diffusion Tensor Imaging (DTI) Diffusion Spectrum Imaging (DSI) Homunculus Map of Human Cortex Homunculus Map of Human Cortex What does the homunculus tell us? • Localization of motor and sensory function • Topographical organization • Cortical representation related to function not mass Cortical Damage • Much of what we know about the cortex comes from studying brain damage • Damage at identifiable sites can produce: • Disorders of planning or social cognition • Apraxias (disorders in action) • Agnosias (disorders in perception) • Aphasias (disorders of language) Case Study: Phineas Gage Disorders of Planning and Social Cognition • Caused by damage to prefrontal area – Disrupts executive control– processes that allow us to direct and regulate our own cognitive activities • e.g., setting priorities, planning, strategizing, ignoring distracters Apraxias • Difficulty in carrying out purposeful movements without the loss of muscle strength or coordination – Disconnection between primary and nonprimary motor areas – Able to carry out each part of a complex movement, but disruption lies in coordination of the movements Agnosias • Visual agnosia: disturbance in recognizing visual stimuli despite the ability to see and describe them – Patient video • Prosopagnosia: inability to recognize faces (fusiform face area) – Patient video – Patient video • Neglect Syndrome: complete inattentiveness to stimuli on one side of the body – Patient video • Akinetopsia: inability to perceive movement – “I see the world in snapshots – like frames of a move but most of the frames are missing” Aphasias • Broca’s Aphasia: disturbance in speech production, caused by damage to Broca’s area – Patient video • Agrammaticism • Anomia • Difficulty with articulation • Wernicke’s Aphasia: disturbance in speech comprehension, caused by damage to Wernicke’s area – Patient video • Disruption in recognition of spoken words • Disruption in comprehension of the meaning of words • Inability to convert thought into words Aphasias Localization of Function • Different regions of the brain serve specialized functions • Sensory Information • Motor Control • Planning and Social Cognition • Perception • Language Connectivity Congenital Prosopagnosics show typical BOLD activation to faces but severe behavioral deficit in face processing DTI show degradation of tracts connecting posterior and anterior regions engaged in face processing (Thomas et al., 2009) Connectivity • Autism – Neurodevelopmental disorder marked by social and communicative deficits and presence of repetitive behaviors • Underconnectivity theory – autism phenotype comes from reduction in global connectivity (long distance connections between frontal and parietal/occipital regions) and increase in local connectivity (particularly in visual areas) Temple Grandin underconnectivity Association cortex – regions not receiving direct sensory input. Involved in perception, language, social and executive functioning. Comparison of human and macaque monkey brain show that major areas of cortical expansion occur in association cortex (Van Essen & Dierker, 2007) Cerebral Cortex • Most projection areas have contralateral organization: – Left hemisphere receives information from right side of body (sensory), or controls right side of body (motor) – Right hemisphere receives information from left side of body (sensory), or controls left side of body (motor) Split Brain Split Brain Split brain patient Phantom Limb Pain • Amputees often feel pain in a limb after it has been removed – Mirror box therapy video • Sensation in limb can be felt when touching other areas of body (most common: lost hand feels touch of face) Neural remapping Plasticity • The brain is plastic—subject to alteration in the way it functions, such as: • Changes in the brain’s overall architecture • The central nervous system can grow new neurons: • But appears unable to do so with cortical injury • This promotes stability in the brain’s connections but is an obstacle to recovery from brain damage. Plasticity • Neurons are subject to alteration in the way they function, such as: • Changes in how much neurotransmitter a presynaptic neuron releases • Changes in neuron sensitivity to neurotransmitters • Creating new connections by growing new dendritic spines Principles and Functions • • • • • • • • • Cephalization All-or-None Law Frequency Coding of Intensity Doctrine of Specific Nerve Energies Localization of Function (+ Integration) Topographic Projection (& Distortion) Split Brain (Crossed Connections) Connectivity & Functional Connectivity Neuro-plasticity & Reorganization