Lecture 6 - cognitive control

inhibition

-can pause behaviour and prevent self from doing things

-behavioural and cognitive inhibition are separate things → but may rely on the same process

cognitive control

-top-down mental processes require effort or attention

-have core and higher order cognitive abilities

core cognitive abilities

-working memory

-inhibitory control

-flexibility

higher order cognitive abilities

-object permanence

-self recognition

-mental time travel

-theory of mind

-tool use/causal reasoning

behavioural inhibition

-stopping actions

-can observe and measure

-response inhibition, deferred gratification, reversal learning

cognitive inhibition

-stopping mental processes → memories, thoughts, perception, emotions

-hard to measure stopping of thoughts

-have overlapping brain areas with behavioural inhibition → evidence from imaging studies and patients of conditions

-can study principles and mechanisms by studying inhibition of motor responses as easier to study behavioural → overriding planned or already initiated actions on behavioural tasks

examples of delayed gratification (behavioural inhibition)

-marshmallow test

-shopping hungry in supermarket

examples of response inhibition (behavioural inhibition)

-stopping responses to stimuli

-could overlap with delayed gratification

examples of reversal learning (behavioural inhibition)

-wisconsin card sorting task

-updating understanding of rules

inhibition and executive function

-voluntary inhibition

-executive functions require one another so that a combination of attention, inhibition and flexibility allows complex behaviour

impulsivity

-result of deficient inhibitory processes

-linked to addiction, ADHD, mania

-response inhibition used as a proxy measure in lab tasks → but only indicates some types of impulsivity

-translational potential of animal studies of response inhibition

reaction times

-time between onset of the stimulus and the onset of response is RT

-delay onset of stimulus for 123ms, 322ms, 277ms

-RT varies across individuals

reaction time distribution

-green square shown at time 0

-300-500ms is standard for RT

-skewed curve, nothing at start then long tail → vary across trials

model for RT

-once race starts at 0 seconds the each runner is described by a linear function of the form: y = ax

• y → current position of the runner - activation of the process

• a → speed of the runner

• x → time

model parameters (model for RT)

-need to specify:

• speed of each runner - slope of each line

• goal line - threshold of when action occurs

-can randomise these parameters in line with expected outcomes

threshold (model for RT)

-for each process can determine the time when it crossed the threshold

-this is model RT

-can then look at the distribution of model RTs over 10,000 processes

-this distribution has a similar shape as the empirical RTs distribution model

neurophysiology of RT variability - overview

-recordings in the frontal eye fields of monkeys performing a RT task

-examination of neurons increasing their firing rate before saccades

-neurons in the frontal cortex indicate the RTs vary due to rate variability in slope of underlying process

-measuring single neuron recording in frontal eye fields in monkey across multiple trials

neurophysiology of RT variability - results

-line shows average firing rate

-time 0 → onset of saccade

-before movement onset, neuron sharply increases firing rate

-no difference in threshold for action between slow trials and fast trials

-differences appears to be in the slope of firing rate increase → reflected in race model

go/nogo task (behavioural methods)

-participant needs to respond to some stimuli (go stimuli) but not to others (nogo stimuli)

-can measure RT and number of correct trials

-signals are arbitrary → people find it easier to respond if it adheres to social conventions

-easy task and general in terms of inhibition

stop signal task (behavioural methods)

-go and stop signals mixed randomly so stop-signal cannot be predicted

-one-key parameter is the stop-signal delay → time between the go and stop signal:

• short-signal delay → response not imminent and easier to inhibit

• long delay → imminent responses harder to inhibit

stop signal reaction time (stop signal task)

-tells us how quickly a participant reacts to the stop signal

-SSRT reaction consists of inhibiting the behavioural response

-means cannot directly measure it because when inhibition is successful there is no response

advanced behavioural measures

-inhibition functions

-could use stop-signal reaction times to calculate probability of motor response based on stop signal delay

intuition for stop signal reaction time

-cannot directly measure the SSRT but can estimate it

-a SSRT of 100ms means that a participants requires 100ms to make use of the stop-signal

-response that occurs later than 100ms after the stop-signal can be stopped

-do know when responses occur based on our RT distribution

failed stops (SSRT)

-RT in failed stop trials are mostly fast, in line with out consideration from the SSRT

three components of stopping (SSRT)

1. stimulus detection

2. action selection

3. inhibition

-used to describe how well an individual can inhibit responses

-SSRT is a measure for reactive inhibition how quickly participants can react to the stop signal

race model of stopping

-people have variability in RTs

-stopping can be modelled as a race between two different types of processes

-the process that reaches the threshold first determines behaviour

1. go process → the response, failure to inhibit

2. stop process → inhibition, successful inhibition

single trial (race model of stopping)

-need to repeat this simulation many times to do a whole experiment

-the slope of the go and stop process are parameters that can vary across trials

-in different trials sometimes the go process and sometimes the stop process wins

stop process winning (race model of stopping)

-stop process has not changed

-it is the go process that had a smaller slope and therefore took longer to reach the threshold

variability in go process (race model of stopping)

-lot of variability in the go process

-less variability in the stop process

-stopping fails for steep go process slopes

-stopping succeeds for small go process slopes

stop-signal delay in race model

-in example stop-signal delay is 250ms → so stop process only starts to increase at time 250ms

-stop process at disadvantage and requires a steeper slope to overtake the go process

-once one of the process reaches the threshold, stop the simulation because the activity afterwards no longer matter

-so the SSRT is the time from the beginning of stop process to when the stop process reaches the threshold (e.g., 210ms-600ms)

strengths of race model

-applied to different animals

-apply to different types of stopping

-different types of stop-signal tasks

-very general as described behaviour and may describe underlying cognitive and neurobiological processes

-allows to model inhibition functions

proactive inhibition

-adjust behaviour in anticipation of potentially having to inhibit a response

-visible as change in the go reaction time

measuring proactive inhibition using stop-signal task

-manipulate the degree of proactive inhibition exerted by the participants by providing information on the probability of the stop-signal

explicit proactive inhibition (stop-signal task)

-provide a specific cue indicating the possibility of the stop-signal occurring

-trial-by-trial or block

implicit proactive inhibition (stop-signal task)

-vary probability across blocks

trial

-a single representation of a stimulus-response sequence

block

-several trials

-typically has specific parameters

session

-consists of one or more blocks

-different sessions are usually separated by longer time intervals

trials per block (proactive inhibition)

-need to determine: number of go trials and stop trials per block

-this yields the percentage of stop trials → stop trials/stop trials + number of go trials

-proactive inhibition is the change in the average RT in go trials between two blocks

steps for measuring proactive inhibition

1. collect all RT from go trials in block 1

2. average them - Mean(RTblock1)

3. repeat for block 2 - Mean(RTblock2)

4. proactive inhibition score = Mean(RTblock2) - Mean(RTblock1)

proactive adjustment hypothesis

-difference between model prediction and empirical data

-proactive inhibition seems to involve adjustments of the response threshold

-doesn’t change the slope of the processes but rather changes the response threshold → increasing the point needed for activation, giving chance for stop process to catch up to go process

parkinsons disease (impaired stopping)

-death of dopaminergic neurons

-severe motor symptoms and less understood cognitive symptoms

-dopamine replacement therapy and DBS

stop-signal task and parkinsons (impaired stopping)

-patients tested on and off levodopa medication

-longer SSRT in patients compared to control but no significant differences between on and off medication

substance dependence (impaired stopping)

-longer SSRTs compared to control group for:

• alcohol users

• meth users

• cocaine users