Psychology Chapter: Nervous System and Neurons

Levels of Analysis

• All psychological phenomena are related to brain activity
• Emotion, perception, attention, memory, reasoning, and conscious experience are all a product of the brain

Nervous System Primer

• The nervous system is comprised of the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS includes the brain and spinal cord
• The PNS includes sensory and motor connections
• The cerebrum (or forebrain) is part of the brain and includes the hemispheres
• The brainstem and cerebellum are also part of the brain

Neuron Structure

• Neurons communicate with other cells via electrical signals
• Neurons receive and transmit messages through electrical impulses, also known as action potentials

Connectional Methods

• The function of a neuron depends on its inputs and outputs
• Connectional methods are used to trace connections to and from a neuron
• Diffusion tensor imaging (DTI) uses MRI to map diffusion of water within neural tissue
• DTI is non-invasive

Correlational Methods

• Correlational methods involve observing brain activity while an individual performs a behavior
• The techniques used are either invasive or less invasive
• Invasive:
  • recording electrical activity of neurons via microelectrodes implanted in the brain
• Less invasive:
  • Electroencephalography (EEG)
  • Magnetoencephalography (MEG)
  • Positron emission tomography (PET)
  • Functional Magnetic Resonance Imaging (fMRI)

Magnetic Resonance Imaging (MRI)

• Differences in tissue properties affect how protons in the tissue behave in a strong magnetic field
• Images are created by partially magnetizing the body using a superconducting magnet

Structural Analysis

• MRI creates clear 3D images of tissue types within the body
• MRI has excellent spatial resolution (accurate localization) on the millimeter scale

Functional Magnetic Resonance Imaging (fMRI)

• Active neurons require oxygen
• fMRI detects changes in the magnetic properties of blood
• fMRI measures the ratio of oxygenated to deoxygenated blood using the blood oxygen level-dependent (BOLD) response

Studying the Damaged Brain

• Neuropsychological testing can be used to study the effects of brain damage on specific cognitive functions
• Lesion methods help us understand the relationship between brain damage and cognition
• Lesions can be caused by traumatic brain injury (TBI), stroke, tumors, degenerative diseases, or infections

Single and Double Dissociations

• Single dissociations compare a patient with a lesion to a control group
• Double dissociations compare two patients with lesions in different brain regions

Deep-brain stimulation (DBS)

• DBS involves implanting electrodes in the brain to stimulate a targeted area with low-voltage electrical currents
• DBS is used to facilitate behavior and treat conditions such as Parkinson’s disease, depression, and OCD

Transcranial magnetic stimulation (TMS)

• TMS uses a magnetic coil placed on the skull to stimulate the underlying brain area
• TMS is used to disrupt cognitive or motor function and can be used to treat depression

Measuring the Brain’s Electrical Activity

• The brain is always electrically active
• Electrical activity can be used to study brain function
• Single-cell recording, EEG, ERPs and MEG are four major techniques used to study the brain’s electrical activity

Single-cell recordings

• Single-cell recordings measure the action potentials of single neurons using fine electrodes
• Electrodes can be placed next to cells (extracellular) or inside cells (intracellular)
• Extracellular recordings can distinguish activity of up to 40 neurons
• Intracellular recordings study a single neuron’s electrical activity
• Single-cell recordings can be used in humans when electrodes are implanted for clinical reasons such as DBS surgery

Electroencephalography (EEG)

• EEG records from thousands of cells revealing features of the brain’s electrical activity
• EEG signal changes with behavior
• EEG recordings from the cortex show a variety of patterns, some of which are rhythmic

Event-related potentials (ERPs)

• ERPs analyze complex EEG waveforms that are related in time to a specific sensory event
• To reduce noise, the stimulus is repeatedly presented and responses are averaged
• ERPs can be visual (VEP), auditory (AEP), motor (MEP), or somatosensory (SEP)
• Averaging the responses reveals a distinctive wave shape

Comparing Neuroscience Research Methods

• Considerations for choosing a research technique include:
  • Temporal resolution (time)
  • Spatial resolution (localization)
  • Invasiveness
  • Cost