12. Goals, Executive Control and Action (1).pdf

Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience 2nd Edition Edited by Bernard J. Baars and Nicole M. Gage 2010 Academic Press Chapter 12 Goals, Executive Control, and Action A case study of Phineas Gage He survived the trauma, but exhibited significant...

Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience 2nd Edition Edited by Bernard J. Baars and Nicole M. Gage 2010 Academic Press Chapter 12 Goals, Executive Control, and Action A case study of Phineas Gage He survived the trauma, but exhibited significant behavioural changes “He is fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires … A child in his intellectual capacity and manifestations, he has the animal passions of a strong man … His mind was radically changed, so decidedly that his friends and acquaintances said he was ‘no longer Gage’.” JM Harlow, Recovery from the passage of an iron bar through the head 1868/1998  Chapter Outline 1.0 Introduction 2.0 Phylogeny and ontogeny 3.0 Function overview 4.0 A closer look at frontal lobes 5.0 A closer look at frontal lobe function 6.0 Neuroimaging the executive brain 7.0 Frontal lobe dysfunction 8.0 A current view of organizing principles of the frontal lobe 9.0 Towards a unified theory of executive control: a conclusion  1.0 Introduction From the silent lobes to the organ of civilization: it took scientists many years to begin to appreciate the importance of the frontal lobes for cognition. Unlike the busy sensory processes that occur in the other lobes, the frontal lobe were not easily linked to any single, easily defined function and were known as ‘the silent lobes’. The concept of executive control is intimately linked to the function of the frontal lobes, however not all functions of the frontal lobe fall under the domain of executive control, and not all executive control functions are subserved by the frontal lobes.  1.0 Introduction Prefrontal cortex can be divided into lateral (side), medial (midline), ventral (bottom), and dorsal (top) regions. The lateral division divides into dorsal and ventral halves separated by a major horizontal fold, the inferior lateral sulcus  2.0 Phylogeny and Ontogeny The prefrontal cortex has expanded over mammalian and primate evolution. A greatly enlarged prefrontal cortex is a distinctively human and primate feature. According to Brodmann (1909), the prefrontal cortex accounts for 29% of total cortex in humans, 17% in the chimp, 11.5% in the macaque, and 3.5% in the cat. While whales and dolphins have large brains, it is the parietal rather than frontal cortex that has expanded in these mammals.  3.0 Function Overview The functions of the frontal lobes defy a simple definition. They are not invested in any single ready-to-label function. Prefrontal cortex plays the central role in forming goals and objectives and then in devising a plan of action required to attain those goals. It selects the cognitive skills needed to implement the plans, coordinates those skills, and applies them in a correct order. Finally, the prefrontal cortex is responsible for evaluating our actions as success or failure relative to our intentions.  4.0 Closer Look at Frontal Lobes How prefrontal cortex is defined A precise definition of prefrontal cortex can be accomplished using Brodmann area maps -- which are based on the types of neurons and connections that are typically found within each area. The prefrontal cortex is comprised of Brodmann areas 8, 9, 10, 11, 12, 13, 44, 45, 46, and 47. A lateral view of the prefrontal cortex, showing Brodmann areas 8, 9, 10, 11, 44, 45, 46, and 47.  4.0 Closer Look at Frontal Lobes How prefrontal cortex is defined A precise definition of prefrontal cortex can be accomplished using Brodmann area maps -- which are based on the types of neurons and connections that are typically found within each area. The prefrontal cortex is comprised of Brodmann areas 8, 9, 10, 11, 12, 13, 44, 45, 46, and 47. A mid-sagittal view of the prefrontal cortex, showing Brodmann areas 8, 9, 10, 11, and 12.  4.0 Closer Look at Frontal Lobes How prefrontal cortex is defined Another method of outlining the prefrontal cortex is through its subcortical projections. The dorsomedial thalamic nucleus is a point of convergence, the ‘summit’ of the integration occurring within the specific thalamic nuclei.  4.0 Closer Look at Frontal Lobes Connectivity for motor control The prefrontal cortex is directly connected with every distinct functional unit of the brain. The three lateral frontal regions of the motor hierarchy (prefrontal, premotor, and motor cortices) are interconnected with the thalamus, basal ganglia, and cerbellum by recurrent axonal loops that are essential for motor control. CM central median nucleus MD mediodorsalis nucleus VA anteroventral nucleus VL ventrolateral nucleus  4.0 Closer Look at Frontal Lobes Using diffusion tensor imaging (DTI) to explore the axonal pathways in the brain The massive connectivity of the frontal lobes is suggested by this tractograph (right panel) of the fiber tracts to Brodmann area 10 (left panel). The red and dark vertical fibers show only the ipsilateral (same hemisphere) connections.. In addition to these fiber tracts, there are many connections between the two hemispheres traveling across the corpus callosum. 4.0 Closer Look at Frontal Lobes Using diffusion tensor imaging (DTI) to explore the axonal pathways in the brain Another view using DTI: a midsagittal view of the fiber bundles is shown in A. The fibers in the prefrontal cortex are shown in green. Note in B how they are organized in the left and right hemispheres, with the frontal lobe shown at the top and the left hemisphere shown on the left side of the figure.  5.0 A Closer Look at Frontal Lobe Function Traditional perspective on frontal lobe function: motor functions, actions, and plans Two broad types of cognitive operations linked to the frontal lobe executive system: 1. An organism’s ability to guide its behavior by internal representations -- the formulation of plans and then guiding behavior according to those plans  5.0 A Closer Look at Frontal Lobe Function Traditional perspective on frontal lobe function: motor functions, actions, and plans Two broad types of cognitive operations linked to the frontal lobe executive system: 2. An organism’s ability not only to guide its behavior by internal representations, but also the capacity of ‘switching gears’ when something unexpected happens  5.0 A Closer Look at Frontal Lobe Function Mental Flexibility To deal effectively in situations that call for ‘switching gears’ requires mental flexibility -- the capacity to respond rapidly to unanticipated environmental contingencies. A task used to assess mental flexibility: the subject must extract the ‘rules’ in order to place the round object in the proper location.  5.0 A Closer Look at Frontal Lobe Function The subject is instructed to place the object in one location (top panel), however he is told that the rule may change at any time during the task. In the first trial, the object is correctly placed and the subject is given feedback that this is correct. The subject repeats that placement in the second trial and again receives feedback that it is correct. In the third trial (bottom panel), the rule has changed and the object must now be placed in the other location. Patients with frontal lobe damage have difficulty in ‘switching gears’ in this type of task.  5.0 A Closer Look at Frontal Lobe Function Executive Control and Social Maturity The capacity for volitional control over one’s actions is not innate, but it emerges gradually through development. It is an important, perhaps central, ingredient of social maturity. Early mother-infant interaction is important for the development of the orbitofrontal cortex during the first months of life.  6.0 Neuroimaging the executive brain Four broad types of cognitive operations linked to the executive systems in the frontal lobes have been extensively investigated using functional neuroimaging techniques such as PET and fMRI. Attention and perception Working memory Executive function Motor control We will summarize findings across these four types of systems in the next slides.  6.0 Neuroimaging the executive brain But first, an important caveat to understanding the results of neuroimaging studies: the prefrontal cortex is intricately involved in many cognitive and executive processes such as paying attention, holding something in mind for a few moments, switching attention when needed, and making decisions. Thus any task used in a neuroimaging study will necessarily involve these complex and overlapping processes in the frontal lobes and throughout other brain regions.  6.0 Neuroimaging the executive brain In order to disentangle the many processes engaged in any task, investigators studying frontal lobe function need to carefully design their studies so that they can identify which processes are specifically related to, for example, attention vs. working memory – processes that are part of performing almost every type of task. Attention and perception Imagine that you are a subject in an fMRI study. Your task is to look at a screen and when you see a picture of a male face, you are to press one button, and if you see a picture of a female face, you press another button. Easy, right? What parts of the brain will be activated by this task? Attention and perception What parts of the brain will be activated by this task? You might suggest that visual cortex (V1) will be activated, based on your knowledge of sensory activity in the brain. You might also suggest that the fusiform face area (FFA) will ‘light up’ since you are looking at human faces (see figures below). Other aspects of your task will activate other regions – the processes of paying attention, making a decision, and pressing a button. These are all key processes that are under the control of the frontal lobes.  6.0 Neuroimaging the executive brain Attention and perception Other aspects of your task will activate other regions – the processes of paying attention, making a decision, and pressing a button. These are all key processes that are under the control of the frontal lobes. Networks of brain activation have been elucidated by Dr. Michael Posner and his colleagues for voluntary attention processes such as alerting to a stimulus, orienting to it, and maintaining executive control. Below, see an example of brain areas active during the time that a subject is alerting to a new stimulus.  6.0 Neuroimaging the executive brain Attention and perception Networks of brain activation have been elucidated by Dr. Michael Posner and his colleagues for voluntary attention processes such as alerting to a stimulus, orienting to it, and maintaining executive control. Here are the networks elucidated for orienting to a stimulus (on left) and then maintaining voluntary attention (on right). Note that the networks activate differing brain regions.  6.0 Neuroimaging the executive brain Working memory The ability to keep something in mind for a limited time is a central function in cognition. This ability – working memory – is closely associated with the voluntary attention systems. In fact, one way of describing working memory is that it serves as an inward directed voluntary attention system. In his book, The Prefrontal Cortex, Fuster (2008) presents a meta-analysis of several neuroimaging studies of working memory to provide a schematic summary of the brain areas involved in experiments tapping visual vs. verbal working memory.  6.0 Neuroimaging the executive brain Working memory Here is a figure from Fuster (2008) showing the key areas of the brain that will be shown to be active in the next figures. Note the experimental time course shown on the bottom of the figure. In this meta-analysis, he focuses on the left hemisphere. Working memory Here is a figure from Fuster (2008) showing brain activity over six stages of time (yellow arrows) in an experiment tapping visual working memory processes. Note that early stages (1) activate visual cortex and then move forward to frontal lobe areas as the experimental trial continues (2-6). Working memory Here is a figure from Fuster (2008) showing brain activity over six stages of time (yellow arrows) in an experiment tapping verbal working memory processes. Note that early stages (1) activate the temporal lobe and then move forward to frontal lobe areas as the experimental trial continues (2-6). Working memory Now compare the patterns of activation for the visual (shown in red shades) and the verbal (shown in yellow shades) working memory tasks. Note the frontal lobe areas that are active in both tasks. Note that sensory regions in the occipital (for the visual memory task) and the temporal (for the verbal memory task) remain activated throughout the experimental trial.  Working memory The perception-action cycle The continued activation of sensory regions observed throughout an experimental trial for visual and verbal working memory tasks in research with humans and with non-human primates has been hypothesized to represent a perception-action cycle of ‘reverberating re-entry’ of information across sensory and motor brain regions. Above is a figure showing brain areas activated in a monkey brain during working memory tasks that tap differing sensory domains: visual, auditory, tactile, and spatial. Similar regions in the frontal lobe are activated across all tasks but the sensory regions differ by specific task.  6.0 Neuroimaging the executive brain Executive function and motor control Executive functions like planning and executing complex behaviors have been studied using the Tower of London task. This task is like a puzzle with many steps for successful completion. In order to solve it, the subject needs to develop a plan. This task activates regions in the dorsolateral prefrontal cortex (DLPFC) (Morris et al., 1993). Interestingly, more DLPFC activity was found for the subjects who found the task difficult.  6.0 Neuroimaging the executive brain Executive function and motor control Another brain region involved in executive function is the anterior cingulate cortex (ACC) – Brodmann area 24. What is its role? One hypothesis is that it serves as an inhibitory effect on the frontal lobes. This inhibitory influence may help us resist being distracted – where as the frontal lobe executive processes are maintaining voluntary attention to the task at hand, the ACC may serve to aid this by inhibiting distractions.  6.0 Neuroimaging the executive brain Executive function and motor control In a summary of the many studies investigating the role of the ACC in human cognition, Bush and colleagues (2000) showed that there were differing activations for the ACC for cognitive tasks (shown in red) vs. emotional tasks (shown in blue).  6.0 Neuroimaging the executive brain Decision Making and Rule Adoption Some daily decisions are rather simple and straightforward, with just one correct solution – such as remembering your friend’s cell phone number or finding the correct answer to a mathematical problem. This is termed veridical decision- making because there is a clear answer. Most decisions made in our daily life, however, are far more complex with no simple – or single – correct. Frontal lobe areas are highly involved in these types of complex decision processes. These types of complex decision processes are termed adaptive decision-making. A key aspect of this type of decision making process if resolving ambiguous aspects of the problem. At the same time, the decision-maker needs to maintain flexibility – to adopt differing perspectives -- in working through the complex decision process.  6.0 Neuroimaging the executive brain Decision Making and Rule Adoption One widely-used method to assess a person’s use of rule adoption – that is, devising short-cuts to making decisions – is the Wisconsin Card Sorting Test. In this test, the cards can be sorted by color, the number of items, their shape, or other features that the experimenter controls. At the beginning of the game, the experimenter determines which matching ‘rule’ [i.e., color, shape] to be used but he does not tell the player what that rule is – the player must learn it through trial and error. During the game, the experimenter changes the rule and again the player must learn what the new rule is through trial and error.  6.0 Neuroimaging the executive brain Decision Making and Rule Adoption One widely-used method to assess a person’s use of rule adoption – that is, devising short-cuts to making decisions – is the Wisconsin Card Sorting Test. This test is a good measure of the player’s mental flexibility – their ability to adapt to new ‘rules’ or circumstances. Mental flexibility is a hallmark of healthy frontal lobe executive function.  7.0 Frontal Lobe Dysfunction The fragile frontal lobes Frontal lobe dysfunction often reflects more than the direct damage to the frontal lobes themselves. The frontal lobes seem to be the bottleneck, the point of convergence of the effects of damage virtually anywhere in the brain. There is a reciprocal relationship between frontal and other brain injuries: damage to the frontal lobes produces wide ripple effects through the whole brain.  7.0 Frontal Lobe Dysfunction Frontal lobe syndromes Damage to different parts of the frontal lobes produces distinct, clinically different syndromes. The most common are dorsolateral and orbitofrontal syndromes.  7.0 Frontal Lobe Dysfunction Frontal lobe syndromes - Dorsolateral Most common symptoms of dorsolateral syndrome are perseverative behavior, field- dependent behavior, and mental rigidity. These patients often typically have a flat affect: an emotionless voice and facial expression. Perseverative behavior: a patient will have an inability to initiate behaviors. Once behaviors are initiated, the patient is equally unable to terminate or change the behavior.  7.0 Frontal Lobe Dysfunction Frontal lobe syndromes - Dorsolateral Field-dependent behavior highlights the distractibility seen with frontal lobe injury. A patient will drink from an empty cup, put on a jacket belonging to someone else, or scribble with a pencil on the table surface, merely because the cup, jacket, and pencil are there, even though these actions make no sense.  7.0 Frontal Lobe Dysfunction Frontal lobe syndromes - Dorsolateral Mental rigidity is a frequent symptom of frontal lobe injury. Mental flexibility is a critical aspect of frontal lobe processing. These patients will show an inability to change their mental state or approach to a problem. The Wisconsin Card Sorting task is frequently used to asses mental rigidity in frontal lobe patients.  7.0 Frontal Lobe Dysfunction Frontal lobe syndromes - Orbitofrontal The orbitofrontal syndrome is in many ways the opposite of dorsolateral syndrome: the patients are behaviorally and emotionally disinhibited. Their affect is rarely neutral, constantly oscillating between euphoria and rage, with impulse control ranging from poor to non-existent. Their ability to inhibit the urge for instant gratification is severely impaired: they do what they feel like doing, when they feel like doing it, without any concern for social taboos or legal prohibitions.  7.0 Frontal Lobe Dysfunction Other clinical conditions associated with frontal lobe damage It is not necessary to have focal damage to the frontal lobes themselves to have prefrontal dysfunction. The frontal lobes are particularly vulnerable in numerous non-focal disorders such as schizophrenia, Tourette’s syndrome, and Attention deficit (hyperactivity) disorder (AD(H)D).  7.0 Frontal Lobe Dysfunction Other clinical conditions associated with frontal lobe damage Attentional functions might may be influenced bu the frontal lobes as well as an ‘attentional loop’ combining frontal, brainstem, and posterior cortex. Breakdown anywhere along this loop may interfere with attention, thus producing a form of attention deficit disorder. Thus, any damage to the prefrontal cortex or its pathways may result in attentional impairment.  8.0 A Current View of the Organizing Principles of the Frontal Lobes Some organizing principles for the frontal lobes have emerged following decades of research with human and non-human primate. 1. The entirety of the cortex of the frontal lobe is devoted to the representation and production of action at all levels of biological complexity. 2. The neuronal substrates for the production of any action is identical to the substrate for its representation. 3. That substrate is organized hierarchically, with the most elementary actions at low levels of the hierarchy, in orbitofrontal and motor cortex, and the most complex and abstract actions in lateral prefrontal cortex. 4. Frontal lobe functions are also organized hierarchically, with simpler functions within, and serving, more global functions. (Fuster, 2008)  8.0 A Current View of the Organizing Principles of the Frontal Lobes A brain schematic for the hierarchical organization of the frontal lobes showing an anterior-posterior organization that is based on the level of abstraction of the action at hand. (Adapted from Badre & D’Esposito, 2007)  9.0 Towards a Unified Theory of Executive Control: A Conclusion After having been overlooked for many decades, executive functions have become the focus of an ever-increasing body of research. A Modular View: one approach has been to ‘fractionate’ executive functions along the familiar lines of sensory modalities (vision vs. audition), linguistic versus non- linguistic, object versus spatial (‘what’ versus ‘where’) distinctions. A Gradient View: a different approach suggests that the functional organization of heteromodal association cortices (such as prefrontal cortex) is interactive and distributed, and not modular. Which approach is the correct one? Only time and future research will tell!