Chapter 2- Cognitive neuroscience Flashcards
Cognitive neuroscience definition
The study of the physiological basis of cognition. Examines localization of function—what areas of the brain control specific skills or
behaviors, neural representations of information, and how different brain areas communicate
Levels of analysis
Refers to the idea that a topic can be studied in a number of different ways, with each approach contributing to its own dimensions of our understanding. For cognitive psychology, levels include the whole brain, to structures within the brain, to chemicals that create electrical signals (neurotransmitters). Just to do routine tasks, many processes must occur at once on different levels of the brain.
Nerve net
What early anatomists saw while looking at stained neurons under the microscope. They believed that neurons formed a continuous network, as microscopes at the time didn’t have a high enough resolution to see individual cells.
Which technique did Golgi develop?
Golgi developed a staining technique, adding silver nitrate to a slice of brain tissue. Only a few cells were stained completely, meaning that they stood out from the rest of the slightly packed cells and their structure was completely visible.
Ramon y Cajal
Used the Golgi stain, but also studied tissue from the brains of newborn animals, as this tissue is less dense. This revealed that the nerve net was not actually continuous and was made up of separate cells. This discovery was called the neuron doctrine
Neuron doctrine
The idea that individual cells transmit signals in the nervous system, and that these cells are not continuous.
3 parts of a neuron
Cell body, axon, dendrites
Cell body
The metabolic center of the neuron that keeps the cell alive. Houses the nucleus and receives information from dendrites
Dendrites
Branch out from the cell body and receive signals from other neurons.
Axon
A long process that transmits signals to other neurons. Ends in an axon terminal and may have a myelin sheath.
Cajal’s conclusions about neurons (3)
- There are small gaps (synapses) between the axon of one neuron and the dendrites/cell body of another neuron.
- Neurons form connections only to specific other neurons. The groups of interconnected neurons form neural circuits.
- There are specialized neurons called receptors outside of the brain
Receptors
Outside of the brain, there are specialized neurons in the eyes, ears, skin, and other areas of the body that detect sensory information from the environment. These neurons are called receptors. They do have axons, but they also have specialized receptors that typical neurons in the brain don’t have.
Edgar Adrian
In the 1920s, Edgar Adrian was the first researcher to record electrical signals from single sensory neurons. He used microelectrodes to record the signals. A recording electrode has its recording tip inside the neuron, and a reference electrode is located a distance away to measure the difference in charge.
Resting membrane potential
The neuron’s resting membrane potential (-70 mV) represents the difference in charge between the inside and outside of the axon. The inside of the neuron is more negative than the outside. Therefore, if the axon is at rest, there will be a -70 mV difference in charge between the two electrodes.
How does membrane potential change as an action potential passes down the axon?
As an action potential passes down the axon, the charge becomes more positive, increasing to +40 mV. The charge will then decrease, becoming more negative until it reaches resting membrane potential. Intense sensations cause action potentials to be fired more quickly.
Do action potentials change in size?
Action potentials do not change in size or shape. This means that the signal will be the shape at the end of the axon as it was at the beginning. Adrian found that when he applied more pressure to a skin receptor, the shape and height of the action potential remained constant, but the number of action potentials traveling down the axon per second increased. A high intensity stimulus will increase the rate of action potentials.
When are neurotransmitters released?
Researchers found that neurotransmitters are released when signals reach the end of the axon. Neurotransmitters transmit the action potentials across the synapse.
Principle of neural representation
Everything a person experiences is based on representations in the person’s nervous system, or information that the brain (or neurons) carries about the organism’s environment.
Which areas of the brain are responsible for vision?
A specific stimulus causes neural firing that is distributed across many areas of the cortex. Therefore, vision is created in many different areas, not just the primary visual cortex. This holds true for multiple other functions, memory included.
Feature detectors
Neurons that respond to specific features of a stimulus, like orientation, movement, and length. Feature detectors are linked to perception- this idea is supported by many experiments. Hubel and Wiesel conducted a visual study on cats and found that each neuron in the visual area of the cortex responded to a specific type of stimulation presented to a small area of the retina.
Experience-dependent plasticity
When the structure of the brain is changed by experience. Example- a kitten’s visual cortex normally contains neurons that respond to all orientations. However, when kittens were raised in an environment that consisted only of verticals, their visual cortex was reshaped so that it only contained neurons responding to verticals. The kittens would ignore horizontal objects. Therefore, they were unable to perceive these objects.
Hierarchical processing
Neurons in the visual cortex that respond to simple stimuli send their axons to higher levels of the visual system, where signals from other neurons combine and interact, and these signals are sent to even higher levels of the brain
Sensory code
Refers to how neurons represent various characteristics of the environment.
Specificity coding
The idea that an object could be represented by the firing of a specialized neuron that responds only to that object. One study found that a single neuron responded to Jennifer Anniston’s face. This idea is likely incorrect. While there are neurons that only respond to faces, each neuron will respond to multiple faces, not just one person. There are also way too many objects to have one neuron dedicated to each.
Population coding
The representation of an object by large groups of neurons firing in a certain pattern. With this idea, each person’s face would be represented by a unique pattern. This would mean a large amount of stimuli could be represented, because large numbers of neurons could create many patterns. However, for some functions, a large number of neurons wouldn’t be necessary.
Sparse coding
Occurs when a particular object is represented by a pattern of firing of only a small group of neurons- the majority of neurons are not participating. With this idea, each person’s face would be represented by a pattern of a few neurons- the patterns would be different, but might overlap with a few other patterns. A particular neuron would respond to more than one stimulus.
Which functions are likely represented by sparse coding?
Code for representing objects in the visual, auditory, and olfactory systems may involve activity across a small group of neurons. Memories are likely also represented by population and sparse coding, with specific patterns of firing representing certain memories.
Localization of function
The idea that specific functions are served by specific areas of the brain. Early evidence of this idea came from neuropsychology.
Cortical equipotentiality
In the 1800s, cortical equipotentiality was widely accepted- the idea that the brain operated as a whole, without any specialized areas.
Broca’s area function
Responsible for production of language.
Broca’s aphasia
These patients were able to say limited amounts of words, or they experienced labored speech with a jumbled sentence structure. Paul Broca’s research on stroke patients with damage to Broca’s area provided evidence for localization of function and challenged the idea of cortical equipotentiality that was prevalent at the time.
Wernicke’s area
An area in the temporal lobe responsible for comprehension of language.
Wernicke’s aphasia
Patients with damage to this area produced fluent and grammatically correct speech, but it would be incoherent (basically the person is just saying random sentences). These patients are unable to match words with their meanings. They are also unable to understand the speech of others.
Which area of the brain is responsible for vision?
The occipital lobe. This is additional evidence for localization of function- studies of soldiers in world war one revealed that damage to occipital lobe resulted in blindness. There was a connection between the damaged area of the occipital lobe and the place in the visual space where the person was blind.
Auditory cortex
The auditory cortex receives signals from the ears and is located in the upper temporal lobe. It is responsible for hearing.
Somatosensory cortex
The somatosensory cortex is located in the parietal lobe. It receives signals from the skin and is responsible for perceptions of touch, pressure, and pain.
Frontal lobe
The frontal lobe receives signals from all of the senses and is responsible for coordination of the senses, as well as higher cognitive functions like thinking and problem solving.
Prosopagnosia
Occurs in people with damage to the temporal lobe on the lower right side of the brain (the FFA). They are unable to recognize faces- they can see faces, they are just unable to recognize whose face it is, even with friends or family members.
Double dissociation
Occurs if damage to one area of the brain causes function A to be absent while function B is present, and damage to another area causes function B to be absent while function A is present. Therefore, two people with brain damage must be found. Ex- one patient with brain damage can’t recognize faces but can recognize objects. A second patient with brain damage in a different area can recognize faces but can’t recognize objects. This lets us conclude that function A and function B are controlled by different mechanisms that operate independently of each other.
How can localization of function be determined using single neurons?
Studies done on animals found that 97 percent of neurons in an area in the temporal lobe responded to faces but not other objects. This area is similar to the face recognition area in humans. Brain imaging studies in humans have determined which areas of the brain are activated by different cognitions.
