intro to cognitive science

Jamuna Subramaniam

Department of Biological Sciences and Bioengineering

Indian Institute of Technology

Kanpur

Intro to Cognitive Science

Higher order brain functions

Language

Learning and memory

Thought

Emotion

Parts of the brain

Diseases led to the discovery of the regions involved in specific functions.

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.

Human brain

The nervous system of a vertebrate

Structure and functional areas of the cerebrum

Brain regions involved in languageLeft lobe

Wernicke’s area

Auditory input - understanding speech

Broca’ s area

Motor output - Indelligible speech

Areas active during different language tasks

Language learning disability Dyslexia

Molecular and cellular network level understanding !!!!!!

NERVOUS SYSTEMS

Three overlapping functions sensory input integration motor output

Interconnected network of neurons

Overview of a vertebrate nervous system

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.

• 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.

Aplysia neuron

• Types of Nerve Circuits.• Single presynaptic neuron → several postsynaptic

neurons.

• Several presynaptic neurons → single postsynaptic neuron.

• Circular paths.

Presynaptic neurons muscles – neuromuscular junctions

Types of neurotransmission

1. Electrical

2. Chemical

• 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

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Measuring Membrane Potentials.


Fig. 48.6a

• An unstimulated cell usually have a resting potential of

70mV.

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.



Fig. 48.7

The basis of the membrane potential

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.


Graded Potentials: Hyperpolarization and Depolarization

• Graded potentials are changes in membrane potential


Hyperpolarization• Gated K+ channels open →

K+ diffuses out of the cell → the membrane potential becomes more negative.


Fig. 48.8a

Depolarization• Gated Na+ channels open →

Na+ diffuses into the cell → the membrane potential becomes less negative.


Fig. 48.8b

• If graded potentials sum to ≈ 55mV a threshold potential is achieved.

• This triggers an action potential.• Axons only.


Fig. 48.8c

The Action Potential: All or Nothing Depolarization

• Step 1: Resting State.


Fig. 48.9

• Step 2: Threshold.


Fig. 48.9

• Step 3: Depolarization phase of the action potential.


Fig. 48.9

• Step 4: Repolarizing phase of the action potential.


Fig. 48.9

• Step 5: Undershoot.


Fig. 48.9


Fig. 48.10

Propagation of the action potential

• 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


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


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

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

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

In vitro patch clamp recording

Nobel Price: Neher and Sakmann, 1991

The Major Known Neurotransmitters

Integration of multiple synaptic inputs

• Summation: graded potentials (EPSPs and IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron.


Fig. 48.14

Action potential generation

Cellular communication at synapse Summation of input

Output action

Biological clock

Emotions

Learning and memory

Human brain

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.


The limbic system (emotions)

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.

Synaptic signaling

1. Fast neurotransmission 2. Slow neurotransmission

Phosphorylation dephosporylation

Signal transduction: Mode of regulation

Second messenger : cAMP, calcium, IP3, cGMP

Figure 11.5 Overview of cell signaling (Layer 3)

Overview of cell signaling (Layer 3)

Figure 11.18 The specificity of cell signaling

Cross talk between different signal cascades

Signal amplification

Learning and memory

A Nobel laureate’s perspective

Eric Kandel

Selection of the problem:

Learning and behavior

easily tractable

Selection of the organism: less complicatedeasy to observe behavior and molecular events

Selection of behavior: Memory storage behavior

Memory storage behavior

Neural circuit

Critical neurons

Cellular and molecular changes in specific neurons

Aplasia marine snail

Aplasia neuron visible to naked eye

Modelbehavior

Gill and siphon withdrawal upon tactile stimuli

Types of memory

Short term: lasts only minutes

Long term: lasts for days

By practice (timed repetition) Short term memory

Long term memory

Behavior taught learned fear

Sensitization shock in the tail, withdrawal of siphon and gill

Neuronal circuit in gill withdrawal

24 mechanosensory neurons integrate siphon skin

6 monosynaptic connection to gill motor neuron

Neurons in in vitro culture

Injection of signal cascade components

Molecular events Involvement of cAMP cascadeSerotonin,

dopamine

Serotonin, dopamine cAMP levels

Modulatory pathway involves cAMP cascade

Sensory neurons release glutamate memory facilitation

Synaptic plasticity

Increase in strength.

Increase in synapse number.

Behavior : Spatial memory

Hippocampal activation

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

• Schizophrenia

• delusions, hallucinations

• Too much of dopamine neurotransmitter signaling.

Diseases of the thought process

Psychiatirc diseases

Spinal cord injury

THANK YOU

intro to cognitive science

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