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.)

inside

outsideNa+ Ca2+

+

-

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)

K+

Cl- +

- inside

outside

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

Synaptic vesicles (SV) Storage of Neurotransmitters

SV Release of Neurotransmitters Binding of Neurotransmitters

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)

Foot

Hip

Trunk

Arm

Hand

Face

Tongue

Larynx

postsynapticneuron

science-education.nih.gov

Flexor-Crossed ExtensorReflex(Sheridan 1900)

Painful Stimulus

Reflex CircuitsWith Inter-neurons

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 neuronsF5 mirror neurons

Gallese et al. 1996

Action observation

Action execution

Shared goal-simulation = Action understandingShared 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

AA Grasping with the mouth

BB Grasping with the cl. hand

CC Grasping with the ipsil. hand

Goal-related neuron in area F5Goal-related neuron in area F5

(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 NeuronsF5 Mirror Neurons

A: Effective Action

B:Mimicked Action

C: Action with tool

Gallese et al. Brain 1996

Umiltà et al. Neuron 2001

A: Full vision to A: Full vision to objectobject

B: Hand fadesB: Hand fades

C: Full vision, no C: Full vision, no objectobject

D: Hand fades, no D: Hand fades, no objectobject

Audio-Visual Mirror NeuronsAudio-Visual Mirror Neurons

Kohler et al. Science (2002)

Vision+Sound

Vision alone

Sound alone

Movement

Murata et al. J Neurophysiol. 78: 2226-2230, 1997

F5 Canonical NeuronsF5 Canonical Neurons

Rizzolatti et al. 1998

A New PictureA New Picture

The fronto-parietal networks

Rizzolatti et al. 1998

F5c-PFF5c-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 goal-related hand actions

and when:

Subject observes another individual performing similar kinds of actions

Somatotopy of Action ObservationSomatotopy of Action Observation

Foot ActionFoot Action

Hand ActionHand Action

Mouth ActionMouth 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

© Stephen E. Palmer, 2002

Cones cone-shaped less sensitive operate in high light color vision

Rods rod-shaped highly sensitive operate at night gray-scale vision

Two types of light-sensitive receptors

cone

rod

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