Executive functions
What region of the brain is central to executive function
Prefrontal cortex is central to executive function.
* The prefrontal cortex is an area that got big in humans compared to animals. It shows our ability to do more complex executive functioning. It reflects the complex ways that we can control behavior, the complex forms of executive control that we have over our behaviour compared to other animals.
What is the frontal lobe involved in?
The two important regions of the prefrontal cortex
Cognitive Control
Stroop test
Miller and Cohen Model of Prefrontal Cortex and Cognitive Control.
In the absence of top-down control from prefrontal cortex, different output pathways compete for expression in response to the stimulus (GREEN). The mapping between the stimulus and saying “green” is strong, so that response is expressed and inhibits the alternative response (“red”).
Miller and Cohen Model of Prefrontal Cortex and Cognitive Control - when you are doing the stroop test.
Prefrontal cortex provides a bias signal that amplifies the selected response (“red”), and results in inhibition of the alternative response (“green”). In this model the prefrontal cortex uses its knowledge of the rules, goals, etc., to direct traffic in other brain regions.
* The Miller and Cohen model is proposing that the two pathways/connections are not in the frontal lobes. That is not what the frontal lobe is doing, the frontal lobes are looking back down on the other parts of the brain and applying this bias.
* The role of the executive function in the frontal lobe is not to actually implement the behavior. The role of the prefrontal cortex is to be a conductor: switch on a pathway and inhibit another pathway.
* The Miller and Cohen model proposes that the lateral prefrontal cortex is actually exerting the control and medial regions of the prefrontal cortex are involved in monitoring the errors.
* The key idea of this model is that the frontal lobes are exerting executive control (top-down control) over sensory motor connections.
The 4 networks involved in cognitive control.
Cognitive control involves interactions between brain networks that connect the prefrontal cortex and the parietal lobes, along with other cortical and subcortical structures.
* Cerebral cortex does not function as a set of discrete areas.
* The cerebral cortex is organized into distributed networks (different regions of the cortex that are sometimes quite far apart from each other but still interacting with each other to form these networks) that regulate cognitive control.
* Frontal lobes are involved in executive function but they arevinteracting with various parts of cerebral cortex in ways that form these dynamic netwroks.
* Connections between these regions are dynamic, they are changing all the time. How they change determines how the brain is interacting with the world.
* There are 4 distinct networks
Default mode network
The default mode network is active when your mind is turned inward. It is involved in your thoughts about yourself, episodic memory, social cognition and mind wandering, i.e., the ongoing internal narrative of your live. The default mode network decreases activity when you reorient attention to engage in the world around you.
* Study where subjects in scanner while doing a task: flash letters and flash words then subtract the difference between the two. This will give you an image of the regions in the brain that are active when reading words.
* It did not matter what the person was doing. Always regions that decreased activity when starting task (compared to person doing nothing) - this is called the default mode network. The colored regions decrease in activity when subjects go from waiting quietly in the scanner to engaging in a cognitively demanding task.
* This network is deactivated when you shift your attention from your inner thoughts to something in the exterior world.
Key cortical nodes of the default mode network
Key cortical nodes of the default mode network are the medial prefrontal cortex, medial parietal lobe (posterior cingulate cortex and precuneus) and the angular gyrus
Key cortical nodes of the default mode network
What happens when you shift your attention from internal thoughts to interacting with the world?
When you shift from your internal thoughts to engage with the world, activity in the default mode network decreases, whereas activity increases in networks (different network:control network) involved in attention and cognitive control.
Control network: top down control
Attention network: allocating attention/directing attention - involved in the top-down attentional control (control what you are attending to).
Bottom up attentional network and the salience network overlap a lot - they may be the same network.
Salience network
The salience network monitors internal and external sensory input and initiates the switch between the default mode and control/attention networks.
* Enables the switching between the attentional and default mode.
- deactivate default mode (stop daydreaming)
- and start directing attention and control.
Together the insula and cingulate cortex make the salience network, its role is to switch between default mode network and control network.
2 elements of Miller and Cohen networks
1) The Controller: exerting the control. Involves the dorsal and lateral regions of cortex.
2) The Error Detector: monitoring errors. Involves Cingulate Cortex.
The insula
Activation in the insula (fMRI)
fMRI images showing activation of right insular cortex in response to
(a) recall- induced anger,
(b) cooling of the hand and
(c) pictures of human faces showing disgust
these 3 experiments (a,b,c) all have in common:
- elicit a certain feeling.
- certain changes in physiology that are associated with this emotion/feeling.
- insula is monitoring body state
- insula is activated indicating something is happening.
From this experiment, we conclude the insula is
- insula is a high order somatic sensory cortex (not a primary sensory area)
- lots of info coming in from your senses (external and internal)
- insula is in charge of the subjective evaluation of sensory stimulus. Ie, place your hand on something hot (the htter = more regions activated). The insula is evaluating the sensory input (mix of your perceived level of heatness and actual experience itself).
- the right insula is important for the subjective experience of your body (ie, pain).
- insula is activated in all of these cases. This is why it is part of the salience network, it is integrating information and sending an alert signal saying something has changed in the environment and that needs to be adressed.
Interoception
The nucleus of the solitary tract:
- found in brainstem
- main input for sensations that are coming from inside your body and from your body’s surface
The parabrachial nucleus is integrating the inputs of these interceptive signals and also regulating outputs that are going out through the autonomic nervous system.
The periaquaductal gray is involved in threat response and plays a role in modulating pain stimulus. Stimulation to the periaqueductal gray or application of opiates diretly is a very powerful analgesic (animals will feel no pain).
Working Memory
The delayed match-to-sample task
The delayed match-to-sample task engages working memory.
* Correct answer: reward (juice or encouragement)
* delay: person holds the image in mind during the delay then has to chose the correct image out of the two options.
*
Neurons in the lateral prefrontal cortex during the delay of the task
Baddeley and Hitch model of working memory
The visuospatial sketch pad:
- hold image in your mind (actively in working memory)
- Involves reactivation, finding stored memory and reactivating those brain regions that are involved.
The Phonological loop:
- comprises a phonological store that is dedicated to working memory and that serves to temporarily hold verbal information.
- ie: saying the phone number over and over again until you have to say it.
- Involves reactivation of an articulatory loop. Inner speech is used to reactivate, or “refresh,” the representations in the phonological store.
Central Executive:
- regulates what is getting loaded into the visual sketch pad and phonological loop based on context.
What systems does working memory involve?
Decision-Making