Chapter 10 - Principles of Neocortical Function Flashcards
What is a hemispherectomy and why may it be performed?
- When one of the hemispheres is removed from the brain
- May be done on those with severe epilepsy, or those with Rasmussen encephalitis
What’s dysphasia?
- A moderate impairment in language
How can hemispherectomy patients function so well?
1) Brain plasticity
2) Levels of function (hierarchy of function from spinal cord to the cortex)
At the level of only the spinal chord, what functions are available?
Reflexes:
- Limb approach to a sensory stimulus
- Limb withdrawal from noxious stimuli
- Stepping movements
At the level of only the hindbrain, what functions are available?
- Perform units of movement when stimulated (ex. hissing, chewing, lapping)
- Exaggerated standing
- Postural reflexes
What are you incapable of performing when limited to the spinal cord?
- No voluntary movement
What are you incapable of performing when only limited to the hindbrain?
- Difficulty maintaining consciousness
- Rigidity (excessive muscle tone)
- Narcolepsy
What does the term low decerebrate indicate?
- Animal is restricted to a hindbrain
What does the term high decerebrate indicate?
- Animal is restricted to a midbrain
What are you incapable of doing when restricted to a midbrain?
- Animal will lack spontaneous and complex behaviours
What are you capable of doing when limited to a midbrain?
- Respond to simple visual and auditory stimulation
- Perform automatic behaviours such as grooming, pouncing on a sound source
- Perform subset of voluntary movements when stimulated
What does the term diencephalic indicate?
- The animal is restricted to the diencephalon
What are you incapable of doing when restricted to the diencephalon?
- Spontaneous behaviour, but hyperactive and aimless (no goal in mind)
- Unchecked emotion (ex. sham rage)
What are you capable of doing when restricted to the diencephalon?
- Sense of smell
- Control over endocrine system and homeostasis
- Behaviour has effect and motivation (i.e., becomes energized and sustained)
What does the term decorticate indicate?
- The animal is restricted to the basal ganglia.
What are you incapable of performing when restricted to the basal ganglia?
- No spatial navigation
- Do not build nests, hoard food
- Difficulty performing skilled movements
What are you capable of doing when restricted to only the basal ganglia?
- Self-maintenance (eating, drinking; can link automatic movements to voluntary movements so behaviours are biologically adaptive)
- Typical sleep-wake cycles
- Perform complex movement sequences in proper order
- Simple learning (ex. classical and operant conditioning)
What does the term typical indicate in an animal?
- The animal has complete access to their cortex and can perform all functions
What major characteristics contribute to the structural organization of the cortex?
-Spiny vs. aspiny neurons
- Layers
- Columns
- Maps
What are spiny neurons?
- They are excitatory neurons
- Around 95% of their excitatory synapses are found on their spines
- Most are pyramidal, some are stellate
What are stellate neurons?
- A type of spiny neuron that has more localized projections, not as extensive as pyramidal cells
Since spiny cells are excitatory, which NT would they be most likely to emit?
- Glutamate
What’s the difference between non-specific afferent connections versus specific afferent connections?
- Non-specific - they terminate across multiple layers of the cortex (more generalized functions)
- Specific - Targets one specific layer of the cortex
T/F: Most interactions between layers take place vertically.
- TRUE
How big are cortical columns?
- Also called modules
- Around 150-300 neurons, forming mini circuits 0.5-2.0 mm wide
Where are cortical columns most prominent?
- More prominent in the sensory cortex
What are cortical maps?
- Areas devoted to processing a specific peripheral unit
- Ex. sensory and motor homunculi, tonotopic representation in A1
- Dozens of maps per sensory modality, processing different aspects of sensory experience
What do more cortical maps usually correlate to?
- Higher intelligence
What is special about Graziano’s cortical maps (2009) compared to Penfields (1930s)?
- They differed primarily in their stimulation protocols
- Graziano stimulated his monkeys for a longer period of time, allowing him to elicit specific actions opposed to simple movements, which is what Penfield did
What’s a multimodal cortex?
- Areas that function in more than one sensory modality
- Also called polymodal
- Contributes to perceptual linking (potential explanation for the binding problem)
What are the two general types of multimodal cortexes?
- Recognizing/identifying/processing info
- Controlling movement related to the above info
What’s the superior temporal sulcus?
- A multimodal cortex associated with processing auditory, visual, and somatosensory info.
What does the term gestalt refer to?
- Perceiving the world as a whole.
How does brain organization translate into our perception of the world as a gestalt?
- Most likely due to intracortical connections among subsets of cortical regions
- Includes column to column interactions
What does the term re-entry signify regarding cortical connections?
- The bidirectional exchange of signals between 2 or more brain areas
- Mechanism by which one area can influence afferent projections received from another area
- NOT the same as feedback
What does Alexander Luria’s (1973) hierarchical model of cortical function claim?
- The cortex can be divided into 2 functional units: posterior cortex; anterior cortex
- Posterior cortex (parietal, occipital, temporal lobes) - a sensory unit; activates paralimbic cortex and amygdala
- Anterior cortex (frontal lobe) - Motor unit; receives projections from posterior cortex, paralimbic, amygdala
- The sensory unit usually starts from primary to secondary to tertiary, while the motor unit is the opposite
According to Luria (1973), summarize the cortical motor system.
- PFC selects a goal/plan
- Premotor cortex organizes appropriate sequence of behaviours
- Primary motor cortex executes the movements
What does Daniel Felleman and David van Essen’s (1991) distributed hierarchical model claim?
- More than one area can occupy a given hierarchical level
- There are reciprocal connections
- Parallel processing occurs
What does the contemporary model of cortical function claim?
- Discrete brain areas do not act as independent processors, rather they function conjointly in large-scale neural networks
- Resting-state fMRI has been used in their discovery
- Cortex is likely made up of primary regions, and multiple large networks forming the association areas
What’s the Default Mode Network (DMN)?
- Responsible for daydreaming, introspection, understanding etc. (passive conditions)
- Involves the PFC, medial temporal lobe, the posterior cingulate cortex, and the posterior parietal lobe
- May be linked to depression (too much rumination)
What are the 4 allegedly unique properties of the human brain?
- Grammatical language
- Phonological imagery
- Theory of mind/social cognition
- Certain forms of intelligence such as intuition
What are some physical properties that may make human brains unique?
- Greater parcellation of cortex (i.e., more maps)
- Higher density of cortical neurons
- Unique classes of cortical neurons
What are von Economo neurons?
- Large bipolar neurons found in areas of cortex associated with social cognition
- Develop late in development, reach adult levels around 4 years of age
- Found in humans and great apes
Which three regions are von Economo neurons found in the brain?
- The dorsolateral prefrontal cortex
- The anterior cingulate cortex
- The frontal insular cortex
*Both emotional hotspots
What’s the difference in function between the anterior cingulate cortex and the frontal insular cortex?
- ACC - Involved in nearly every complex cognitive function (empathy, impulse control, emotion, decision-making)
- Insula - play a more specific role in social emotion and self-awareness (empathy, trust, guilt, humor, etc.)
What did John Allman (2005) theorize about von Economo neurons?
- Thought that VENS are associated with the emergence of theory of mind
- Speculated that VENs fail to develop normally in people with ASD (although it has been found that people with ASD may have too many)
- VENs may allow rapid (intuitive) adjustment to changing social contexts
- Implicated in several neuropsychiatric illnesses including frontotemporal dementia, schizophrenia, bipolar disorder
