Download - Intro to Cognitive Science
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Jamuna Subramaniam
Department of Biological Sciences and Bioengineering
Indian Institute of Technology
Kanpur
Intro to Cognitive Science
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Higher order brain functions
Language
Learning and memory
Thought
Emotion
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Parts of the brain
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Diseases led to the discovery of the regions involved in specific functions.
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Brain imaging
EEG collecting the peripheral brain electrical activity
PET positron emission tomography – radioactive tracers in the water deutrium more active areas more blood flow increased radiotracersignalIndividual neurotransmitters –radiotracers –receptor binding,occupancy and turnover molecular level studies possible at the systems level in humans.
MRI&fMRIBased on bloodflow – paramagnetic property of hemoglobinActive brain regions oxygen bound blood flow will be higher.
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MRI
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Human brain
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The nervous system of a vertebrate
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Structure and functional areas of the cerebrum
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Brain regions involved in languageLeft lobe
Wernicke’s area
Auditory input - understanding speech
Broca’ s area
Motor output - Indelligible speech
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Areas active during different language tasks
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Language learning disability Dyslexia
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Molecular and cellular network level understanding !!!!!!
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NERVOUS SYSTEMS
Three overlapping functions sensory input integration motor output
Interconnected network of neurons
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Overview of a vertebrate nervous system
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Networks of neurons with intricate connections form nervous systems
• Neuron Structure and Synapses.
• The neuron is the structural and functional unit of the nervous system.
• Nerve impulses are conducted along a neuron.
• Dendrite → cell body → axon hillock → axon
• Some axons are insulated by a myelin sheath.
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• Axon endings are called synaptic terminals.
• They contain neurotransmitters which conduct a signal across a synapse. A synapse is the junction between a presynaptic and postsynaptic cell.
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Aplysia neuron
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• Types of Nerve Circuits.• Single presynaptic neuron → several postsynaptic
neurons.
• Several presynaptic neurons → single postsynaptic neuron.
• Circular paths.
Presynaptic neurons muscles – neuromuscular junctions
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Types of neurotransmission
1. Electrical
2. Chemical
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• A membrane potential is a localized electrical
gradient across the membrane.
• Anions are more concentrated within a cell.
• Cations are more concentrated in the extracellular fluid.
Every cell has a voltage, or membrane potential, across its plasma membrane
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• Measuring Membrane Potentials.
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Fig. 48.6a
• An unstimulated cell usually have a resting potential of
70mV.
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How a Cell Maintains a Membrane Potential?• Cations
• K+ is the principal intracellular cation.
• Na+ is the principal extracellular cation.
• Anions
• Proteins, amino acids, sulfate, and phosphate are the principal intracellular anions.
• Cl– is the principal extracellular anion.
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Fig. 48.7
The basis of the membrane potential
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Types of gated ion channels• Chemicallygated ion channels open or close in response
to a chemical stimulus.
• Voltagegated ion channels open or close in response to a change in membrane potential.
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Graded Potentials: Hyperpolarization and Depolarization
• Graded potentials are changes in membrane potential
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Hyperpolarization• Gated K+ channels open →
K+ diffuses out of the cell → the membrane potential becomes more negative.
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Fig. 48.8a
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Depolarization• Gated Na+ channels open →
Na+ diffuses into the cell → the membrane potential becomes less negative.
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Fig. 48.8b
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• If graded potentials sum to ≈ 55mV a threshold potential is achieved.
• This triggers an action potential.• Axons only.
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Fig. 48.8c
The Action Potential: All or Nothing Depolarization
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• Step 1: Resting State.
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Fig. 48.9
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• Step 2: Threshold.
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Fig. 48.9
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• Step 3: Depolarization phase of the action potential.
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Fig. 48.9
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• Step 4: Repolarizing phase of the action potential.
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Fig. 48.9
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• Step 5: Undershoot.
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Fig. 48.9
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Fig. 48.10
Propagation of the action potential
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• Electrical Synapses
• Action potentials travel directly from the presynaptic to the postsynaptic cells via gap junctions.
Chemical or electrical communication between cells occurs at synapses
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Chemical Synapses
• More common than electrical synapses.
• Postsynaptic chemicallygated channels exist for ions such as Na+, K+, and Cl.
• Depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize.
• Brought about by binding of neurotransmitters released from the presynaptic terminal to the postsynaptically localized chemicallygated channels
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Fundamental currencies of the living cell
DNA/RNA string of nucleotides nitrogenous base (four different bases pentose sugar and phosphate)
Protein : string of amino acids (20 different amino acids) secondary,tertiary and quarternary structures
DNA
RNA
Protein
NH2(CH)nCOOH
R
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Excitatory neurotransmission
Positive event brings about membrane depolarization action potential generation – an action happening
Major excitatory neurotransmitter in the CNS: glutamate
Glutamate receptors : Ionotrophic (Na+ channel coupled) functional receptor complex is multimeric Three different types: Kainate, AMPA and NMDA receptors
Diseases : conitnous firing excitotoxicity neuronal death in stroke, epilepsy
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Inhibitory neurotransmissionHyperpolarization – modulates – no action potential generation
Inhibitory anion : Cl
Inhibitory neurotransmitter : GABA gammaaminobutyric acid
GABAA receptor complex pentameric – several types of subunits: alpha, beta, gamma, delta and rho – subunit subtypes.
Have modulatory sites – anesthetics, antianxiety drugs
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In vitro patch clamp recording
Nobel Price: Neher and Sakmann, 1991
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The Major Known Neurotransmitters
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Integration of multiple synaptic inputs
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• Summation: graded potentials (EPSPs and IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron.
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Fig. 48.14
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Action potential generation
Cellular communication at synapse Summation of input
Output action
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Biological clock
Emotions
Learning and memory
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Human brain
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The Hypothalamus and Circadian Rhythms
The biological clock is the internal timekeeper.
• The clock’s rhythm usually does not exactly match environmental events.
• Experiments in which humans have been deprived of external cues have shown that biological clock has a period of about 25 hours.
• In mammals, the hypothalamic suprachiasmatic nuclei (SCN) function as a biological clock.
• Produce proteins in response to light/dark cycles.
• This, and other biological clocks, may be responsive to hormonal release, hunger, and various external stimuli.
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The limbic system (emotions)
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Learning and memory
Shortterm memory stored in the frontal lobes.The establishment of longterm memory involves the hippocampus.The transfer of information from shortterm to longterm memory is enhanced by repetition (remember that when you are preparing for an exam).Influenced by emotional states mediated by the amygdala.Influenced by association with previously stored information.
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Synaptic signaling
1. Fast neurotransmission 2. Slow neurotransmission
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Phosphorylation dephosporylation
Signal transduction: Mode of regulation
Second messenger : cAMP, calcium, IP3, cGMP
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Figure 11.5 Overview of cell signaling (Layer 3)
Overview of cell signaling (Layer 3)
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Figure 11.18 The specificity of cell signaling
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Cross talk between different signal cascades
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Signal amplification
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Learning and memory
A Nobel laureate’s perspective
Eric Kandel
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Selection of the problem:
Learning and behavior
easily tractable
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Selection of the organism: less complicatedeasy to observe behavior and molecular events
Selection of behavior: Memory storage behavior
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Memory storage behavior
Neural circuit
Critical neurons
Cellular and molecular changes in specific neurons
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Aplasia marine snail
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Aplasia neuron visible to naked eye
Modelbehavior
Gill and siphon withdrawal upon tactile stimuli
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Types of memory
Short term: lasts only minutes
Long term: lasts for days
By practice (timed repetition) Short term memory
Long term memory
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Behavior taught learned fear
Sensitization shock in the tail, withdrawal of siphon and gill
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Neuronal circuit in gill withdrawal
24 mechanosensory neurons integrate siphon skin
6 monosynaptic connection to gill motor neuron
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Neurons in in vitro culture
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Injection of signal cascade components
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Molecular events Involvement of cAMP cascadeSerotonin,
dopamine
Serotonin, dopamine cAMP levels
Modulatory pathway involves cAMP cascade
Sensory neurons release glutamate memory facilitation
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Synaptic plasticity
Increase in strength.
Increase in synapse number.
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Behavior : Spatial memory
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Hippocampal activation
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Diseases of Cognition
Dementia – Loss of memory
Alzheimer’s diseaseCerebral cortex and hippocampus; Amyloid plague accumulation. Most prevalent – Complex neurodegenerative disease defects in the neurotransmitter acetylcholine and glutamate !
Huntington’s disease
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• Schizophrenia
• delusions, hallucinations
• Too much of dopamine neurotransmitter signaling.
Diseases of the thought process
Psychiatirc diseases
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Spinal cord injury
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