Chapter 2 Cognitive Neuroscience Some Questions to Consider

Chapter 2 Cognitive Neuroscience

Some Questions to Consider • What is cognitive neuroscience, and why is it • • • necessary? How is information transmitted from one place to another in the nervous system? How are things in the environment, such as faces and trees, represented in the brain? Is it possible to read a person’s mind by measuring the activity of the person’s brain?

Building Blocks of the Nervous System • Neurons: cells specialized to receive and transmit information in the nervous system • Each neuron has a cell body, an axon, and dendrites

Building Blocks of the Nervous System • Cell body: contains mechanisms to keep cell alive • Axon: tube filled with fluid that transmits electrical signal to other neurons

Building Blocks of the Nervous System • Dendrites: multiple branches reaching from the cell body, which receives information from other neurons – Sensory receptors: specialized to respond to information received from the senses

Caption: A portion of the brain that has been treated with Golgi stains shows the shapes of a few neurons. The arrow points to a neuron’s cell body. The thin lines are dendrites or axons.

Caption: Basic components of the neuron. The on the left contains a receptor, which is specialized to receive information from the environment (in this case, pressure that would occur from being touched on the skin). This neuron synapses on the neuron on the right, which has a cell body instead of a receptor.

How Neurons Communicate • Action potential – Neuron receives signal from environment – Information travels down the axon of that neuron to the dendrites of another neuron

How Neurons Communicate • Measuring action potentials – Microelectrodes pick up electrical signal – Placed near axon – Active for ~1 second

Caption: (a) Action potentials are recorded from neurons with tiny microelectrodes that are positioned inside or right next to the neuron’s axon. These potentials are displayed on the screen of an oscilloscope and are also sent to a computer for analysis. (b) An action potential recorded by a microelectrode looks like this. The inside of the axon becomes more positive, then goes back to the original level, all within 1 millisecond (1/1, 000 second). (c) A number of action potentials displayed on an expanded time scale, so a single action potential appears as a “spike”.

How Neurons Communicate • Measuring action potentials – The size is not measured; size remains consistent – The rate of firing is measured • Low intensities: slow firing • High intensities: fast firing

Caption: Records showing action potentials in a neuron that responds to light entering the eye. (a) Presenting light causes an increase in firing; (b) increasing the light intensity increases the rate of firing further; and (c) even more light results in a high rate of firing.

How Neurons Communicate • Synapse: space between axon of one neuron and dendrite of another • When the action potential reaches the end of the axon, synaptic vesicles open and release chemical neurotransmitters • Neurotransmitters cross the synapse and bind with the receiving dendrites

How Neurons Communicate • Neurotransmitters: chemicals that affect the electrical signal of the receiving neuron – Excitatory: increases chance neuron will fire – Inhibitory: decreases chance neuron will fire

How Neurons Process Information • Not all signals received lead to action • • potential The cell membrane processes the number of impulses received An action potential results only if the threshold level is reached – Interaction of excitation and inhibition

Localization of Function • Specific functions are served by specific areas of the brain • Cognitive functioning breaks down in specific ways when areas of the brain are damaged • Cerebral cortex (3 -mm thick layer that covers the brain) contains mechanisms responsible for most of our cognitive functions

Lobes of the Cerebral Cortex • Frontal – Reasoning and planning – Language, thought, memory, motor functioning • Parietal – Touch, temperature, pain, and pressure • Temporal – Auditory and perceptual processing – Language, hearing, memory, perceiving forms • Occipital – Visual processing

Localization of Function: Limbic System • Hippocampus: forming memories • Amygdala: emotions and emotional memories • Thalamus: processing information from vision, hearing, and touch senses

Localization of Function: Perception • Primary receiving areas for the senses • – Occipital lobe: vision – Parietal lobe: touch, temperature, pain – Temporal lobe: hearing, taste, smell Coordination of information received from all senses – Frontal lobe

Localization of Function: Perception • Fusiform face area (FFA) responds specifically to faces – Temporal lobe – Damage to this area causes prosopagnosia (inability to recognize faces) • Parahippocampal place area (PPA) responds specifically to places (indoor/outdoor scenes) – Temporal lobe • Extrastriate body area (EBA) responds specifically to pictures of bodies and parts of bodies

Caption: (a) The parahippocampal place area is activated by places (top row) but not by other stimuli (bottom row). (b) The extrastriate body area is activated by bodies (top), but not by other stimuli (bottom).

Localization of Function: Language • Language production is impaired by damage to Broca’s area – Frontal lobe • Language comprehension is impaired by damage to Wernicke’s area – Temporal lobe

Caption: Broca’s and Wernicke’s areas were identified in early research as being specialized for language production and comprehension.

Distributed Processing in the Brain • In addition to localization of function, specific • functions are processed by many different areas of the brain Many different areas may contribute to a function

Caption: As this person watches the red ball roll by, different properties of the ball activate different areas of his cortex. These areas are in separate locations, although there is communication between them.

Method: Brain Imaging • Positron Emission Tomography (PET) – Blood flow increases in areas of the brain activated by a cognitive task – Radioactive tracer is injected into person’s bloodstream – Measures signal from tracer at each location of the brain – Higher signals indicate higher levels of brain activity

Caption: (a) Person in a brain scanner. (b) In this cross section of the brain, areas of the brain that are activated are indicated by the colors. Increases in activation are indicated by red and yellow, decreases by blue and green

Method: Brain Imaging • Subtraction technique measures brain activity before and during stimulation presentation • Difference between activation determines what areas of the brain are active during manipulation

Caption: The subtraction technique used to interpret the results of brain imaging experiments.

Method: Brain Imaging • Functional Magnetic Resonance Imaging (f. MRI) – Subtraction technique – Measures blood flow through magnetic properties of blood – Advantage: no radioactive tracer needed

Method: Event-Related Potential (ERP) • Neuron “firing” is an electrical event • Measure electrical activity on the scalp and • • • make inferences about underlying brain activity Averaged over a large number of trials to calculate ERPs Advantage: continuous and rapid measurements Disadvantage: does not give precise location

Caption: (a) Person wearing electrodes for recording the eventrelated potential (ERP). (b) An ERP to the phrase “The cats won’t eat. ”

Representation in the Brain • Feature detectors: neurons that respond best to a specific stimulus • Hubel & Wiesel (1965) – Simple cells: neurons that respond best to bars of light of a particular orientation – Complex cells: neurons that respond best to an oriented bar of light with a specific length

Caption: Three types of stimuli that Hubel and Wiesel (1959, 1965) found caused neurons in the cat cortex to respond. Neurons responded to bars with a specific orientation, to bars with a specific orientation moving in a particular direction, and bars of a particular length moving in a particular direction. Neurons that responded to these specific types of stimuli were called feature detectors.

Representation in the Brain • Specificity coding: representation of a specific stimulus by firing of specifically tuned neurons specialized to just respond to a specific stimulus • Distributed coding: representation by a pattern of firing across a number of neurons

Caption: How faces could be coded by specificity coding. Each faces causes one specialized neuron to respond. Caption: How faces could be coded by distributed coding. Each face causes all the neurons to fire, but the pattern of firing is different for each face. One advantage of this method of coding is that many faces could be represented by the firing of the three neurons.