CHAPTER 2: Cognitive Neuroscience

#228b22 = VOCABULARY

#9D00FF = DATES/TIME PERIODS

#FFA500 = “Subconcepts/Ideas”

Blue Color on Here = People

INTRODUCTION

• COGNTIVE NEUROSCIENCE: Field concerned with studying the neural basis of cognition

LEVELS of ANALYSIS

• LEVELS OF ANALYSIS: A topic can be understood by studying it at a number of different levels of a system

  • Basically, it's studying a topic in different ways, with each approach adding a unique dimension to our understanding

• You can use the analogy of a car to explain the "levels of analysis." We can understand a car by testing its performance (like measuring behavior in cognition). We gain deeper insight by looking at its engine and systems (like studying the brain's physiology). Even more detail comes from examining internal processes (like looking at brain structures and chemicals). Analyzing the car at these different levels gives a fuller understanding, just as studying cognition at behavioral, physiological, and neural levels provides a more comprehensive view.

  • So, understanding a car at different levels (performance, mechanics, internal processes) is analogous to studying cognition at different levels (behavior, physiology, neural activity), with each level providing a deeper understanding.

• The illustration exemplifies how perception and memory can be analyzed at four physiological levels, from basic chemical reactions to the coordinated activity of large brain regions, using Gil and Mary as an example.

  

  • PERCEPTION: Chemical processes activate neurons, then brain structures, then groups of structures, resulting in the perception of Mary

  • MEMORY: Chemical processes activate neurons, leading to brain storage, which is later activated for the memory of Mary

    • Both processes demonstrate how understanding perception and memory involves examining physiological events at multiple levels, from chemical reactions to large-scale brain activity

NEURONS: BASIC PRINCIPLES

• Brain appears to be static

• NEURON(S): Cell that is specialized to receive and transmit information in the nervous system

EARLY CONCEPTIONS OF NEURONS

THE NERVE NET + GOLGI'S CONTRIBUTIONS

• NERVE NET: A network of continuously interconnected nerve fibers (as contrasted with neural networks, in which fibers are connected by synapses)

  • In the 19th century, staining revealed a "nerve net" initially believed to be a continuous pathway for uninterrupted signal transmission, but early observation limitations made it appear continuous, obscuring the detailed structure

• 1870s: Camillo Golgi's (1843-1926) silver nitrate staining technique revolutionized brain research by selectively staining a small number of cells in their entirety, providing a much clearer view of individual neural structures compared to previous methods

CAJAL + THE NEURON DOCTRINE: INDIVIDUAL CELLS + NEURAL SIGNALING

• NEURON DOCTRINE: The idea that individual cells called neurons transmit signals in the nervous system, and that these cells are not continuous with other cells as proposed by nerve net theory (States that individual cells transmit signals in the nervous system)

• Spanish physiologist Ramon y Cajal (1852-1934) investigated the nerve net using two key techniques:

  • THE GOLGI STAIN: Selectively stained a small number of brain cells

  • STUDYING BRAIN TISSUE: He studied brain tissue from newborn animals, which has a lower cell density compared to adult brains

    • Methods showed the nerve net wasn't continuous ‒ the brain is made of connected neurons

      • Finding formed the basis of the neuron doctrine

      • NOTE: This contrasts with the nerve net theory, which proposed a continuous network of cells

    • Basically, Cajal revealed that the nerve net was not a continuous structure but rather composed of individual, connected units called neurons, a discovery that formed the basis of the neuron doctrine stating individual cells transmit nervous system signals, contrasting with the earlier nerve net theory

• Cajal's made some additional conclusions about neurons:

  • There is a small gap between the axon of one neuron and the dendrites or cell body of another neuron ‒ gap is called a synapse

  • Neurons do not connect randomly but form specific connections with other neurons

  • These specific connections form groups of interconnected neurons, known as neural circuits

  • Beyond the brain, there are specialized neurons that gather information from the environment, such as those found in the eye, ear, and skin

• Cajal's idea of individual neurons communicating via synapses to form neural circuits is considered foundational to understanding how the brain creates cognitions, making him "the person who made this cellular study of mental life possible"

BASIC PARTS OF A NEURON

• CELL BODY: Part of a cell that contains mechanisms that keep the cell alive. In some neurons, the cell body and the dendrites associated with it receive information from other neurons

  • Basically, it is the metabolic center of the neuron

• DENDRITES: Structures that branch out from the cell body to receive electrical signals from other neurons

• AXONS (NERVE FIBERS): Part of the neuron that transmits signals from the cell body to the synapse at the end of the axon

• SYNAPSE: Beyond the brain, there are specialized neurons that gather information from the environment, such as those found in the eye, ear, and skin

• NEURAL CIRCUITS: Group of interconnected neurons that are responsible for neural processing

• RECEPTORS: Specialized neural structures that respond to environmental stimuli such as light, mechanical stimulation, or chemical stimuli

• So, the neuron has a receiveing end and a transmitting end, and it's role is to transmit signals

THE SIGNALS THAT TRAVEL in NEURONS

• The exact nature of neuron signals required powerful amplifiers, developed in the 1920s

• Edgar Adrian (1889-1977) used microelectrodes to record electrical signals from single sensory neurons, winning the 1932 Nobel Prize

  • This recording setup involves a microelectrode inside the neuron and a distant reference electrode

  • The charge difference is amplified and displayed, revealing the neuron's electrical activity

• MICROELECTRODES: Small wires that are used to record electrical signals from single neurons.

  • RECORDING ELECTRODE: When used to study neural functioning, a very thin glass or metal probe that can pick up electrical signals from single neurons

  • REFERENCE ELECTRODE: Used in conjunction with a recording electrode to measure the difference in charge between the two. Reference electrodes are generally placed where the electrical signal remains constant, so any change in charge between the recording and reference electrodes reflects events happening near the tip of the recording electrode

• RESTING POTENTIAL: Difference in charge between the inside and outside of a nerve fiber when the fiber is at rest (no other electrical signals are present)

• NERVE IMPULSE: An electrical response that is propagated down the length of an axon (nerve fiber) ‒ also know as a action potential

• ACTION POTENTIAL: Propagated electrical potential responsible for transmitting neural information and for communication between neurons. Typically travel down a neuron’s axon

FROM NERVE NET to NEURON DOCTRINE

• RESTING POTENTIAL

  • Axon at Rest: Potential difference = -70 mV (inside more negative than outside)

  • Maintained when no signals present

• ACTION POTENTIAL (NERVE IMPULSE)

  • Stimulation of neuron receptor triggers impulse down axon

  • As impulse passes electrode: Inside charge rises to +40 mV (compared to outside)

  • Charge then reverses, becomes negative again

  • Returns to resting potential

  • Duration: ~1 millisecond

• OBSERVATION

  • Multiple action potentials can travel past an electrode (represented by vertical lines on compressed time scale)

• SIGNIFICANCE

  • Action potential is the primary mechanism for information transmission in the nervous system

  • Focus is on action potential, though other electrical signals exist