Ionotropic Receptors
Postsynaptic potentials
Depending on the type of ion channel
which opens, the postsynaptic cell
membrane becomes either depolarized or
hyperpolarized.
 Ions will tend to follow the concentration
gradient from high to low concentration,
and the electrostatic gradient towards
the opposite charge.

Excitatory postsynaptic
potentials (EPSPs)
Opening of ion channels which leads to
depolarization makes an action potential more likely,
hence “excitatory PSPs”: EPSPs.


Inside of post-synaptic cell becomes less negative.
Na+ channels (NB remember the action potential)
Ca2+ . (Also activates structural intracellular changes ->
learning.)
Na+
Ca2+
-

+

outside
inside
Inhibitory postsynaptic
potentials (IPSPs)
Opening of ion channels which leads to
hyperpolarization makes an action potential less
likely, hence “inhibitory PSPs”: IPSPs.


Inside of post-synaptic cell becomes more negative.
K+ (NB remember termination of the action potential)
Cl- (if already depolarized)
Cl-
K+
-

+

outside
inside
Postsynaptic Ion motion
Neuronal firing: the action
potential
The action potential is a rapid
depolarization of the membrane.
 It starts at the axon hillock and passes
quickly along the axon.
 The membrane is quickly repolarized to
allow subsequent firing.

Requirements at the synapse
For the synapse to work properly, six basic events need to happen:
 Production of the Neurotransmitters


Storage of Neurotransmitters




SV
Release of Neurotransmitters
Binding of Neurotransmitters


Synaptic vesicles (SV)
Lock and key
Generation of a New Action Potential
Removal of Neurotransmitters from the Synapse

reuptake
Overview
Course introduction
 Neural Processing: Basic Issues
 Neural Communication: Basics
 Vision, Motor Control: Models

Motor Control Basics
• Reflex Circuits
– Usually Brain-stem, spinal cord based
– Interneurons control reflex behavior
– Central Pattern Generators
• Cortical Control
Hierarchical Organization of
Motor System
• Primary Motor Cortex and Premotor Areas
Primary motor cortex (M1)
Hip
Trunk
Arm
Hand
Foot
Face
Tongue
Larynx
postsynaptic
neuron
science-education.nih.gov
FlexorCrossed
Extensor
Reflex
(Sheridan
1900)
Reflex
Circuits
With
Inter-neurons
Painful Stimulus
Gaits of the cat: an informal computational model
Vision and Action
The discovery of mirror neurons in the frontal lobes of
monkeys, and their potential relevance to human brain
evolution — which I speculate on in this essay — is the
single most important "unreported" (or at least,
unpublicized) story of the decade. I predict that mirror
neurons will do for psychology what DNA did for biology:
they will provide a unifying framework and help explain a
host of mental abilities that have hitherto remained
mysterious and inaccessible to experiments.
Ramachandran, Reality Club Lecture 2001
1. What are mirror neurons?
2. What is the promise? Why the excitement?
3. What challenges are faced in fulfilling that promise?
F5 mirror neurons
Action
observation
Action
execution
Gallese et al. 1996
Shared goal-simulation = Action understanding
Representations in the premotor cortex (Rizzolatti et al).
Shift from thinking about movement representations
to action representations.
Neurons in F4, F5 coding action primitives such as
grasping, pinching, pulling
Goal-related neuron in area F5
A Grasping with the mouth
B Grasping with the cl. hand
C Grasping with the ipsil. hand
(Rizzolatti et al. 1988)
90’s: Shift to perceptual responses of F5 neurons
Three classes of neurons
1. movement/action neurons
Respond only when animal moves
2. “canonical” neurons
Respond when object is presented alone
3. mirror neurons
Respond when observing action towards
object.
Same neurons activated during production
and perception of an action.
F5 Mirror Neurons
A: Effective Action
B:Mimicked Action
C: Action with tool
Gallese et al. Brain 1996
A: Full vision to object
B: Hand fades
C: Full vision, no object
D: Hand fades, no object
Umiltà et al. Neuron 2001
Audio-Visual Mirror Neurons
Vision+Sound
Vision alone
Sound alone
Movement
Kohler et al. Science (2002)
F5 Canonical Neurons
Murata et al. J Neurophysiol. 78: 2226-2230, 1997
A New Picture
Rizzolatti et al. 1998
The fronto-parietal networks
Rizzolatti et al. 1998
F5c-PF
Rizzolatti et al. 1998
The F5c-PF circuit
Links premotor area F5c and parietal area PF (or 7b).
Contains mirror neurons.
Mirror neurons discharge when:
Subject (a monkey) performs various types of goalrelated hand actions
and when:
Subject observes another
similar kinds of actions
individual
performing
Somatotopy of Action Observation
Foot Action
Hand Action
Mouth Action
Buccino et al. Eur J Neurosci 2001
MEG study comparing pianists and non-pianists.
Pianists show activation in primary motor cortex when listening
to piano.
Activation is specific to fingers used to play the notes.
Colored region: MEG signal for pianists minus non-pianists.
Vision
Overview of the Visual System
Physiology of Color Vision
Two types of light-sensitive receptors
Cones
cone-shaped
less sensitive
operate in high light
color vision
Rods
rod-shaped
highly sensitive
operate at night
gray-scale vision
© Stephen E. Palmer, 2002
The Microscopic View
How They
Fire
• No stimuli:
– both fire at base rate
• Stimuli in center:
– ON-center-OFF-surround
fires rapidly
– OFF-center-ON-surround
doesn’t fire
• Stimuli in surround:
– OFF-center-ON-surround
fires rapidly
– ON-center-OFF-surround
doesn’t fire
• Stimuli in both regions:
– both fire slowly