Class Web Site

• Go to www.uleth.ca ->current students -> class websites -> NEUR 3680A ->Class Website

• You will find the course outline as well as lecture slides there

Reading associated with upcoming lectures

• Read chapter 1 for historical overview

• Today’s lecture comes from chapter 2 - use the lecture to guide your reading, this chapter is in much more detail than you need for this course

• We will discuss techniques, especially neuroimaging, which is found in chapters 3 and 4

Goals and Methods

What is the goal of Cognitive Neuroscience?

Goals and Methods

• Broad goal is to understand how the brain accomplishes cognitive processes such as attention, memory, language and consciousness

Goals and Methods

• But there are some smaller steps that we need to take:– HOW: how do neurons work (physiology)

and how do they interact to form circuits?– WHERE: for a given cognitive task, where

are the neurons that do that job

Structure of Neurons

• The Neuron Doctrine– brain was originally thought to be one

continuous mesh of connected soma (Camillio Golgi)

– Modern view: Brain is composed of discrete cells (Santiago Ramon y Cajal)

Structure of Neurons

– Basic parts of the neuron

– Cell Body contains DNA, manufactures proteins, energy, “decides” whether to send signal to next neuron

Structure of Neurons

– Basic parts of the neuron

– Dendrites receive input from other neurons, transmit “passive” potential to cell body

Structure of Neurons

– Basic parts of the neuron

– Axon conducts signal from cell body to other neurons

Neurons are electrically active

• Membrane dynamically swaps charges (ions)

• At “rest” positive charges accumulate on outside, negative on the inside…how?

Neurons are electrically active

• Selective permeability plus Na+/K+ pump

Neurons are electrically active

• If a neuron must use ATP to maintain its charge, what does it mean for the brain to be “active” or “inactive”?

Neurons are electrically active

• Two kinds of membrane potentials: graded potential vs. action potential

Neurons are electrically active

• Graded potential– stimulation (usually a post-synaptic potential) causes Na+ to

enter the cell, depolarizing the membrane– Na+ disperses along membrane, spreading depolarization

that decreases in strength with distance

Neurons are electrically active

• Importance of Graded Potential– graded potentials “sum” to determine if

neuron will transmit signal (analog computation)

Neurons are electrically active

• Importance of Graded Potential– Electroencephalography

(EEG) measures graded potentials

– depolarization at one end of cell body leads to extracellular currents that can be measured on the scalp!

Neurons are electrically active

• Action Potential occurs when voltage-gated channels open

Neurons are electrically active

• Action Potential occurs when voltage-gated channels open

• Voltage-Gated channels are clustered where axon and cell body meet (axon hillock) and along the axon

Neurons are electrically active

• Opening of voltage-gated channels triggers an “active” propagation of depolarization along the length of the axon

Neurons are electrically active

• Importance of the Action Potential– AP “spikes” can be measured with electrodes

placed beside the cell - a powerful tool in measuring neural responses to various stimuli

Neurons are electrically active

• Importance of the Action Potential– Action Potential is “all-or-nothing” (digital

computation)

The synapse and neurotransmitters

• Signals “jump” from one neuron to another at the synapse

The synapse and neurotransmitters

• Arrival of AP triggers influx of Calcium ions

• Neurotransmitter is released and diffuses across cleft

• Receptor molecules on post-synaptic side allow Na+ to enter

The synapse and neurotransmitters

• Importance of the synapse and neurotransmitters– neurotransmitters have different functions and are

associated with specific circuits in the brain– e.g. dopamine has a role in learning and in

addiction; norepinephrine plays a role in attention

The synapse and neurotransmitters

• Importance of the synapse and neurotransmitters– The synapse is the site of action of most

psychoactive drugs– e.g. stimulants (e.g. cocaine, amphetamine) act on

dopamine, depressants (e.g. alcohol) act on GABA

The synapse and neurotransmitters

• Importance of the synapse and neurotransmitters– Brain can “reprogram” itself by adjusting the

efficacy of synapses - important difference between brains and (current) computers

The synapse and neurotransmitters

• Gap Junctions are direct electrical connections between neurons– thought to be faster than normal synapses– some connections in the retina are gap junctions

The Role of Glia

• Glia outnumber neurons 10 to 1 !• Believed to perform “support” roles

– guidance during development– “plumbing” and maintaining the blood-

brain barrier (fMRI)– mylination

• More recently thought to play a direct role in cognitive function– glia have electrically active membranes– may enter into electrical circuits with

neurons via gap junctions