Download Cognitive control I

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Cognitive Control
Man cannot live without self-control
– Isaac Bashevis Singer
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Cognitive control I
Cognitive control is
 The ability of our thoughts and actions to rise above mere reactions to the
immediate environment and be proactive.

To anticipate possible futures and to coordinate and direct thought and action to
them (goal-directed behavior).

a hallmark of intelligent behavior.
The prefrontal cortex (PFC), seems to play a central role in cognition. It is the
cortical area that reaches the greatest relative size in the human brain and is
thus thought to be the neural instantiation of the mental qualities that we think of
as “intelligent.”
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Cognitive control II
The cognitive control system must also have the ability to select which sensory,
memory, and motor processes are activated at a given moment. → Attention
The neural system for cognitive control must have

The infrastructure and mechanisms for selecting goal-relevant, and
suppressing goal-irrelevant, processes throughout the cerebral cortex.

A way to deal with the gaps in time that are inevitable with goal-directed
behaviors.
The ability to keep goal-relevant information online and available for processing is
called working memory.
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Cognitive control III
Finally, and perhaps most importantly, the cognitive control system must be highly
plastic and flexible.
Virtually all voluntary, goal-directed behaviors are acquired by experience, and given
that humans and other primates are capable of rapid learning of new volitional
behaviors, the cognitive control system must have an equal capacity for rapid
learning.
Goal-directed behaviors can also be temporarily interrupted and resumed at
ease. One might temporarily divert oneself from wine shopping, for example, to
pick up some cheese. By contrast, automatic behaviors are characterized by their
rigidity.
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Areas of the frontal lobe. The prefrontal cortex includes all of the areas in front of the
primary and secondary motor areas
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The PFC occupies a far greater
proportion of the human
cerebral cortex than in other
animals, suggesting that it might
contribute to those elusive
cognitive capacities that
separate humans from animals.
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Anatomy and organization of the prefrontal cortex
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PFC: the silent cortex
Unlike electrical stimulation of more posterior regions that produce hallucinations
or motoric responses, stimulation of the PFC produces no obvious effect. This led it
to be termed silent cortex.
PFC damage has remarkably little overt effect; patients can perceive and
move, there is little impairment in their memory, and they can appear remarkably
normal in casual conversation.
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Distinguishing between stored knowledge and activated information
• We have unbounded capacity in long-term memory, but very
limited ability to keep information active is severely limited
• Early work on memory emphasized that short-term memory was
to assist in the translation of newly acquired information into a
format for longer-term storage.
• More recently work has reconceptualized the function role of a
different form of short-term memory -- the working memory.
• Working memory system has been suggested as the processes
that represent the current contents of cognition.
• Patricia Goldman-Rakic has called working memory the
“blackboard of the mind.”
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Prefrontal cortex is necessary
for working memory but not
associative memory
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• A working memory / recognition memory task requires monkeys to pick a
previously unselected object
• Monkeys with lesions that encompassed areas 46 and 9 of the DLPFC had
selectively impaired working memories.
• In a control experiment, monkeys received frontal lesions in the vicinity of
areas 6 and 8. These animals performed well in both versions of the task.
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• Children younger than 1 year are unable to accomplish a similar
working memory task.
• The child acts as though the object is “out of sight, out of mind.”
• The ability to succeed in this type of tasks parallels the development of
the frontal lobes.
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Physiological correlates of working memory
• In the working memory tasks, it is not enough for a stimulus to be
recognized; subjects need to retain a record of its relevance
• To conditions for working memory system: First, it should have a
mechanism to access stored information; second: there should
be a way to keep the information active
Prefrontal neurons can show sustained activity during delayed-response tasks
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The sustained activity could reflect either sensory information related to the cue or
movement information related to the behavioral response. Both are found in the
PFC, each with different temporal characteristics.
PFC delay activity has been shown to convey a wide range of behaviorally relevant
cues: objects, colors, sounds, the frequency of a vibration to the hand, and
forthcoming eye and arm movements.
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Earl Miller conducted a series of experiments to determine the specificity of
prefrontal neurons
Two possibilities:
•Prefrontal neurons simply provide a generic signal that supports
representation in other cortical areas
•Prefrontal neurons code specific stimulus features
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Firing profile of a neuron that shows a preference for one object over another
during the “what” delay
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Firing profile of a neuron that shows a preference for one location (“where”
neuron)
There are also “what-where” neurons!
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The selectivity of PFC neurons are task specific
• In these studies, the cell activity is dependent on the monkey’s using that
information to obtain a response
• If the animal is required simply to passively view the stimuli, the response
of these cells is minimal and the persistent activity during the delay period is
absent.
• If the task conditions change, the same cell become responsive to a new
set of stimuli
But, maybe these activities represent a mechanism for maintaining
motor responses?
• The activity of these cells is modified by past experience.
• Fewer sustained responses are observed in an untrained animal
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Two hypotheses of the role of PFC:
•PFC maintains working memory as
well as stores long-term memory
•PFC are a temporary repository for
representations accessed from other
neural sites
PFC is connected intimately with
post-sensory regions of the
temporal and parietal cortices
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• PFC response sensitive to working memory demand
• Lower FFA response during delay period
• FFA leads PFC during encoding
• PFC leads FFA during retrieval
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Three components are essential for successfully executing an
action plan:
1.One must identify the goal the develop subgoals
2.In choosing among goals, consequences must be anticipated
3.One must determine what is required to achieve the subgoals
• Failure to achieve a goal can happen in many ways
• The failures of goal-oriented behavior in patients with prefrontal
lesions can be traced to many potential sources
• They often provide unreasonable solutions
• They demonstrate a certain inflexibility in their decision making
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• Cognitive control provides the interface through which goals influence
behavior
• Complex actions require that we maintain our current goal
• Focusing on the information that is relevant to achieving that goal
• Ignoring irrelevant information
• Shift from on subgoal to another in a coordinated manner
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Dynamic filtering mechanism
Working memory is more than passive
sustaining of representations; it
requires an attentional component in
which the subject’s goals modify the
salience of sources of information
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Inhibitory control of sensory
responses
Evoked potentials reveal filtering
deficits in patients with lesions in the
lateral prefrontal cortex.
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Humans with Frontal Damage Are
Disinhibited
The patients are unable to inhibit sorting by
the previous rule.
This inability to ignore irrelevant stimuli
and the actions they trigger has led PFC
patients to be described as stimulusbound, and the disruption of the patient’s
ability to think and plan has been termed
goal neglect
Wisconsin Card Sorting Task
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Humans with Frontal Damage Have Difficulty in Planning
Prefrontal patients have a great deal of difficulty planning and organizing their lives.
Wilder Penfield, a neurosurgeon during the mid-twentieth century described the case
of his sister, on whom he operated to remove a large frontal tumor. Prior to the
surgery she had been an excellent cook, and though her basic culinary skills
remained subsequent to the operation, she seemed unable to organize her behavior
so that all the elements of the meal were ready simultaneously.
The Tower of London Test
→ requires the patient to think several
moves in advance
Patients with prefrontal damage are
greatly impaired at this task, making
many more moves than necessary to
reach the fi nal goal position.
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Thinking outside the (match) box
Functional fixedness
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Top-down control may also involve the amplification of task-relevant
information
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The task goal, specified by the instruction, can modulate perceptual
processing by either amplifying task-relevant information or inhibiting taskirrelevant information.
However, the data do not reveal if this modulation is the result of prefrontal
activation
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In an extension of the study comparing healthy elders and young people,
researchers found:
• Older subjects showed only an enhancement effect
• They did not show the suppression effect in either FFA or PPA.
• The result suggests that enhancement and suppression involve different
neural mechanisms
• Aging disproportionately affect prefrontal function
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The medial frontal cortex as a monitoring system
• ACC was assumed to be a component of the limbic system, helping to
modulate autonomic responses during painful or threatening situations.
• The medial frontal cortex, especially the anterior cingulate cortex (ACC)
is now recognized as a critical component of a monitoring system.
• Medial frontal cortex is engaged whenever a task becomes more
difficult
• Activation of ACC increases when the subjects make mistakes
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Interactions between the medial and lateral frontal cortex to facilitate goaloriented behavior.
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Disinhibition in behavioral control
One of the most striking features of prefrontal patients is their disinhibition
and lack of behavioral control. The patients are often impulsive, quick to
anger, and prone to making rude and childish remarks.
An example of disinhibition is utilization behavior. During a medical examination,
a patient with PFC damage will pick up and use items that have been left on the
doctor’s desk.
The ability of disinhibition can be tested using the Stroop test
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