Cognitive Neuroscience

What are we doing with our brains right now?

• Feeling your chair

• Squirming (moving)

• Watching

• Listening

• Remembering

• Paying attention

• Sleeping

• Feeling anxious

• Feeling hungry

• What happens when you ask a question?

The Brain

• Approx 3lbs• 1 trillion cells• 100 billion neurons• ½ of neurons are in cerebellum• Each neuron has 5000 – 10,000 synapses• Males and females differ, but only slightly• Neurons transmit signals at speed of about 2 m/s• There are more possible connections in your brain

than there are atoms in the universe

Cognitive Neurosccience

• The cell

• Cortex

• Mid-Brain

• Hindbrain

Cell Structure: From an Information Processing View

Dendrites receive signals.Signals travel along the Soma or Cell Body and Summate at the Axon HillockThe signal must be above a Threshold for the signal to travel down the Axon

Dendrites – Receive in Modulate signals Omnidirectionally – They are graded potentials – they decay as they travel

Soma– Where the signals are summed– The amplitude and the timing (concurrence) are important– The signal strength must be greater than the resistance at the axon hillock– The threshold can shift– The soma has a baseline

• Baseline indicates all is normal• Indicates cell is alive

– Firing is not perfect, Noise: can fire for no reason, or not fire when it “should”

Cell Structure: From an Information Processing View

Axons – Transmit signals in one direction and are ballistic

(all or nothing)– Have myelin sheaths which sustain the signal

strengths (do not decay)– Their axon buttons or knobs release

neurotransmitters

Cell Structure: From an Information Processing View

Afferent or sensory neuron: conduct impulses from the sensory organs to the central nervous system (brain and spinal cord)

Efferent or motor neuron: conduct impulses from the central nervous system to the effector organs (such as muscles and glands) are called motor (or efferent) neurons

Interneurons (also known as connector neurons or association neurons): connect sensory neurons to motor neurons.

Functional classification

Quizz

The dendrite is part of the neuron which

a) Is covered in myelin sheath

b) Propagates signals in one direction only

c) Receives modulated signals

d) Releases neurotransmitters

The glial cells• maintain the ionic environment• modulate nerve signal propagation • controls the uptake of

neurotransmitters• Protect by surrounding and buffering• Speed transmission by forming myelin

sheaths

Functional classification

Quizz

Glial cells have numerous functions. Which one of these is NOT one of its functions.

a) To produce myelin sheathing

b) Protect by surrounding and buffering

c) Summing signals to trigger an action potentials

d) A and C

Think About This

• Each cell has a criteria for firing

• criteria shift

• No one neuron firing is sufficient information, the meaning is in the average rate in a given population.

Thinking MachinesPinker, How the Mind Works

• How do you get neurons to represent simple logical functions?

• By setting the threshold

• This requires pre-wiring

• But cannot pre-wire for every thing in the world like mouse or justice.

Thinking MachinesPinker, How the Mind Works

• Instead of one-neuron-one-symbol the brain uses distributed representation

• Many categories combined (e.g., crispy, green, edible) sum up to create one value (e.g., celery)

Thinking MachinesPinker, How the Mind Works

• Turn the network upside down, and you can represent the fuzzy quality of logic where tokens can be more or less good examples of a category.

• Here the item tomato only lights up some of the qualities for fruit

Thinking MachinesPinker, How the Mind Works

• The neuron at the top is removed and the correlations amongst the nodes is preserved.

• The everything-connects-to-everything is called auto-associator, and has five features in common with human pattern recognition.

Thinking MachinesPinker, How the Mind Works

• Five features of Auto-associators1. Reconstructive and content addressable memory

– Specifying an item in memory automatically lights up a copy or version of that memory anywhere else. If you light one part of the network, if the weights are strong enough, the parts will light up. So you can recognize a word that has ‘mudsplashes’ on it.

2. Graceful degradation. Do not discard the whole percept because of one faulty piece of information (e.g., PRITN, HELF)

3. Constraint satisfaction. – Sinned a pin does not make sense. – But send a pen does even though the sounds are very similar.– With logic you have to test each possibility. With auto-associator

the context is intrinsic to the network, and the most meaningful evaluation emerges. Ambiguities are allowed: Necker Cube.

Thinking MachinesPinker, How the Mind Works

• Five features of Auto-associators4. Generalizes automatically.

– E.g., bottom row is distributed pattern for an animal (parrot). The top row are the features of the category the animal belongs to (feathers, beak, flies). The relationship amongst the features of a category have an intrinsic correlation.

5. Learn from examples, where learning is a change in the weights.

White Matter and Grey Matter

What is the Order of Intelligence? Why?

Rabbit

Raccoon

Cat

Camel

Kangaroo Baboon Monkey Human

Forebrain

Function of Limbic System

Hindbrain

Lobes of the Cerebral Cortex

• Frontal– Reasoning & Planning

• Parietal– Touch, Temperature, Pain, &

Pressure

• Temporal– Auditory & Perceptual processing

• Occipital– Visual processing

The Cortex“The Bark”

Prefrontal Cortex

• Recall the order of things

• Provides the brakes on impulse control– Damage can produce

Tourette’s like symptoms of tic or exclaiming obscenities

Story of Phineas Gage: Damage to the Prefrontal cortex

Gage was fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operations, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. A child in his intellectual capacity and manifestations, he has the animal passions of a strong man. Previous to his injury, although untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart businessman, very energetic and persistent in executing all his plans of operation. In this regard his mind was radically changed, so decidedly that his friends and acquaintances said he was 'no longer Gage.’

Testing the Prefrontal cortex: The Wisconsin Card Sorting task

• The patient is told to sort the cards, but they are not told how to sort.

• But they are told if they matched the cards correctly.

• They must use their memory for the order of things to figure out the rules of the sorting.

• It took an entire manual to score the test, nowadays it is done on the computer.

Primary Somatosensory and Motorsensory Cortex