Chapter 2 Cognitive Psychology Flashcards
(46 cards)
Neuron
Neurons are the basic unit of the brain and the nervous system.
The brain contains approximately 80-100 billion neurons.
During pregnancy, about 250,000 neurons are generated every minute (Ackerman, 1992).
There are an estimated 10-100 trillion connections (synapses) between these neurons.
Components of a Neuron
Cell Body: Maintains the neuron’s health, including nutrition and metabolism.
Dendrites: Receive electrochemical signals (information) from other neurons.
Axons: Transmit electrochemical signals (information) to other neurons
Neurons and Information Processing:
Neurons handle all information processing.
Input: Information from senses like vision, hearing, smell, taste, and touch.
Afferent neurons: Carry sensory information to the Central Nervous System (CNS).
Motor Output: Actions like movement and speech.
Efferent neurons: Transmit motor commands from the CNS to muscles.
Processing/Storage/Analysis: Happens in the brain, mainly using interneurons.
Neural Communication:
Neurons communicate despite not physically touching; they have gaps called synapses.
Neurons produce electrical signals called action potentials.
Communication between neurons occurs through chemical signals known as neurotransmitters.
Thus, neural communication is fundamentally electrochemical in nature.
Action Potential:
Neurons have a resting potential of around -70mV (millivolts) compared to the outside.
1 mV is equal to 1/1000 of a volt.
When a neuron’s receptor is stimulated, it depolarizes to around +40 mV compared to the outside.
After firing a signal, the neuron returns to its resting potential through repolarization.
Action potential, Electrical Activity in Neurons:
Electrical Activity in Neurons:
Resting Potential: Neuron is at its baseline, around -70mV.
Depolarization: Neuron becomes more positive (e.g., +40mV) during stimulation.
Repolarization: Neuron returns to its resting potential after firing.
Return to Resting Potential: The neuron settles back to its normal -70mV.
Action Potentials (AP): Each AP lasts about 1 millisecond (1/1000 of a second).
Neurons can fire around 500-800 APs per second.
Action potentials: All-or-None Principle:
All-or-None Principle:
Once an Action Potential (AP) is triggered, it travels along the axon without changes in strength.
Similar to a bullet leaving a gun.
The strength of the AP does not change based on the intensity of the stimulus.
Intense stimuli are represented by a higher rate of firing, not a stronger AP.
Think of it like a few or several bullets firing, not larger or smaller bullets, or faster or slower bullets.
Action Potentials (AP):Level of skin stimulation:
Action Potentials (AP):
Level of skin stimulation:
Mild stimulation (A)
Medium stimulation (B)
Strong stimulation (C)
The size of the AP does not change.
However, the number of APs does, depending on the strength of the stimulus.
More APs fire in response to stronger stimulation, but the individual APs remain the same size.
Neurons and Information Representation:
Neurons have a baseline level of activation, known as spontaneous activity.
Stimuli can either increase or decrease this baseline activity.
Neurons convey different information through multiple pathways.
Despite sending a single unvarying signal (Action Potential), they affect other neurons in diverse ways.
This leads to the question: How do neurons influence one another?
Neural Transmission:
Neurons do not physically touch each other; they have small gaps known as synapses.
Communication between neurons occurs through the transmission of chemical messengers (neurotransmitters) from the pre-synaptic neuron (PreSN) to the post-synaptic neuron (PSN).
At the synapse, the communication switches from electrical to chemical transmission.
Neurotransmission Process:
Neurotransmitters are released by synaptic vesicles in the Pre-SN.
They are received by receptor sites on the PSN.
Each receptor site only binds to specific types of neurotransmitters, similar to locks and keys.
Consequently, there are several classes of neurotransmitters, each with different functions.
Excitatory Effects of Neurotransmitters:
Excitatory neurotransmitters result in the depolarization of the post-synaptic neuron (PSN), making it more likely to fire an action potential (AP).
When enough excitation occurs, often from multiple pre-synaptic neurons, the threshold for firing an AP is reached.
The function of a neurotransmitter depends on its type, the location of its action, and other factors.
For example, glutamate is associated with learning, while dopamine plays a role in addiction and reward processing.
Psychopharmacological Drugs and Neurotransmitters:
Many psychopharmacological drugs work by altering neurotransmitter (NT) function.
Examples include Selective Serotonin Reuptake Inhibitors (SSRIs) in Major Depressive Disorder (MDD).
Dopamine antagonists are used in the treatment of psychosis.
Most illegal drugs have addictive potential due to their effects on NT systems, such as methamphetamine and cocaine, which are dopamine (DA) agonists.
Post-Synaptic Neuron (PSN) Function:
The PSN either fires or doesn’t fire based on the combined excitatory and inhibitory effects of all pre-synaptic neurons.
A complex network of neurons allows for information processing and flexibility of action.
This enables the brain to respond selectively rather than passively reacting to every stimulus, such as someone asking for your name.
Sensory Coding - Specificity Coding Limitations:
Specificity coding, where unique neurons represent each sensory detail, has limitations.
It would require an enormous number of neurons to represent everything we perceive, which is impractical.
For example, representing every variation of an apple (varieties, colors, shapes, sizes, half-eaten, etc.) would be infeasible.
Neurons constantly die, which would result in a random loss of perception and memory.
Therefore, it’s unlikely to be the primary way information is represented in the brain.
Population Coding:
Each object is represented by the firing of all neurons in a network.
Robust to the loss of individual neurons because the pattern of activation remains the same.
Can represent many different aspects of an object, such as different orientations, colors, and shapes of an apple, etc.
Limitations of Population Coding:
It may require a substantial number of neurons and complex neural networks.
Understanding how the brain precisely decodes and interprets population-coded information is challenging.
The neural circuits involved in population coding are not fully understood, and the mechanism is still an active area of research.
Population Coding: Limitations
Expensive
* Wiring cost
* Energy utilization
* Cumbersome (prone to errors)
* Memory (confusing phone numbers)
Sparse Coding:
In sparse coding, an object is represented by the pattern of firing of a subset of neurons, while others remain silent.
This coding method is used to represent information in various sensory systems, including visual, auditory, and olfactory.
For example, it can be applied to represent the pitch of a sound, where specific neurons fire to represent particular pitch values while others stay quiet.
Types of Coding in the Brain:
All three types of coding (specificity coding, population coding, and sparse coding) are used in the brain.
Population coding and sparse coding are commonly employed in processes such as perception, reasoning, and memory. These coding methods enable the brain to efficiently represent and process information in different contexts.
Levels of Analysis for Cognitive Functions:
Crash Course on Neurons: Understanding the basics of how individual neurons function.
Levels of Analysis: Examining cognitive functions from various perspectives.
Neuronal Representation: Investigating how neurons or sets of neurons represent information at the micro level.
Localized Representation: Studying how specific brain regions represent information at a localized, regional level.
Distributed Representation: Exploring how multiple brain regions work together to represent information at a broader scale.
Neural Networks: Understanding how large networks of interconnected brain regions collectively represent and process information.
Localized Representation:
Localized representation involves the concept of localization of function, where specific functions are served by particular areas of the brain.
For example, there is a distinct brain area known as the fusiform area responsible for processing faces.
Broca’s area (Brodmann Area 44) is another localized brain region involved in language production. It was famously identified through the case of Patient Tan, who could only utter the word “tan,” as documented by Paul Broca in 1861.
- What is the deficit in Broca’s
aphasia?
- Slow, labored, ungrammatical
speech due to damage
(stroke/injury) in Broca’s area - But able to convey some content
What is the deficit in Wernicke’s
aphasia?
The deficit in Wernicke’s aphasia is characterized by fluent and grammatically correct speech, but it is often incoherent. Individuals with Wernicke’s aphasia have difficulty understanding other people’s speech, matching words with their meanings, and using the rules of grammar. In essence, while Broca’s patients struggle to use grammar, Wernicke’s patients have difficulty conveying meaningful and coherent language.
