March 11, 2021
PSY 340 Brain and Behavior
Class 13: Brodmann Areas & Large-Scale Brain Networks (Outline)
1. fMRI (Functional Magnetic Resonance Imaging): see notes from last class
2. DTI (Diffusion Tensor Imaging) aka Diffusion MRI
- Measuring the diffusion (flow) of water in tissue: how fast and in what direction?
- Isotropy (flows freely in any direction) vs. anisotropy (constained flow in only certain directions)
- Water found most frequently in white matter of the brain.
- Direction of flow ("fractional anisotrophy") can be color coded in DTI along the X, Y, & Z axis
- Tractography: studying the different tracks of white matter fibers in the brain.
= the attempt to construct a comprehensive map of the neural connections in the brain. Connectome is parallel to the use of term "genome" for the full complement of human genes.
Problem of how detailed the connectome can be?
Large Scale Networks in the Brain
Structural connections: anatomical links
Functional-Dynamic connections: actual interactions between neural elements in the brain
The Functional Networks
There is some disagreement over how many major networks function in the brain. The list below indicate the 8 networks that most researchers have come to regard as most important.
- Default Mode Network (DMN): sometimes called the "Task-Negative Network"
- Salience Network (SALN)
- Executive Control Network (ECN) or Fronto-Parietal Network [FPN]
- Dorsal Attention Network (DAN)
- Ventral Attention Network (VAN)
- Auditory Network (AUDN)
- Visual Network (VISN)
- Motor-Tactile Network (MTN) or Somatosensory Network
Default Mode Network (DMN) ["Task-Negative Network"]
- Discovered ca. 2001 by observing the patterns of oxygen use in brains during fMRI studies when participants were (1) actively doing something vs. (2) quietly "resting" in between tasks.
- Distinctive pattern of action when the brain was "at rest"
- Functions of the DMN
- Spontaneous thinking (daydreaming)
- Internally-directed thought; self-referential thought
- Autobiographical self (episodic memory), reflecting on
- Decision making about the future (recalling past & thinking ahead)
- Mentalizing: Reflecting on what others are thinking & trying to understand their thoughts, feelings, intentions, etc.
- The DMN develops across childhood into early adulthood
- Damage/Dysfunction of DMN
- ? possibly involved in Autism Spectrum Disorders
- Hyperactive DMN is associated with
- schizophrenia (overly intensive self-reference; impairments in attention & working memory)
- depression (negative rumination: constant dwelling on negative matters in thinking)
Salience Network (SALN)
- The SALN gives a person the ability to sift through the various external and internal stimuli and identify what is most important at that moment (= what is most salient).
- This network integrates the various stimuli which come from the senses monitoring the outside world (visual, auditory, somatosensory, etc.) with the data that report what is happening within the individual's body (e.g., autonomic nervous system arousal, feelings of pleasure or pain, hunger, etc.).
- In doing so, the SALN signals when the person's behavior has to change, e.g., it's time to eat...to study...to run away from danger...to turn on a different television channel, etc.
- The SALN is associated with the anterior cingulate cortex (ACC), presupplementary motor areas (preSMA), and the anterior insula (AI).
Executive Control Network (ECN) or Fronto-Parietal Network (FPN)
- The ECN/FPN deploys sustained attention and working memory to process the sensory-motor data it is receiving and both chooses to respond in a selective and particular way while suppressing responses which it finds irrelevant or erroneous.
- Damage/dysfunction ==> "Dysexecutive Syndrome"
- Cognitive problems with short and long-term memory; understanding how to deal with problems in dailylife; short attention span; cognitive flexibility
- Emotional problems in speaking or responding inappropriately; anger, aggression, high levels of frustration
- Behavioral problems of interacting with others socially, following social norms, etc.
Dorsal Attention Network (DAN): when we choose to pay attention to something
- "Top-down" process of selecting or attending to important visual and spatial information; detecting new or novel features of the environment
Ventral Attention Network (VAN): when something around us suddenly grabs our attention
- "Bottom-up" process that responds to unexpected or suddenly appearing stimuli in the environment; stimuli which "catch our attention" are monitored and acted upon by the VAN
The three major sensory-motor networks involve
Auditory Network (AUDN)
Visual Network (VISN)
Motor-Tactile Network (MTN; aka Sensory-Motor Network [SMN])