Chapter 16: The Frontal Lobes and Networks PDF

4/25/24 1 Chapter 16 The Frontal Lobes and Networks 2 Learning Objectives Describe the anatomy of the frontal lobes Explain the theory of frontal-lobe function Summarize the executive functions of the frontal-lobe networks Describe the symptoms of frontal-lobe lesions Explain the relationship betwee...

4/25/24 1 Chapter 16 The Frontal Lobes and Networks 2 Learning Objectives Describe the anatomy of the frontal lobes Explain the theory of frontal-lobe function Summarize the executive functions of the frontal-lobe networks Describe the symptoms of frontal-lobe lesions Explain the relationship between intelligence and the frontal lobes 3 Portrait: Losing Frontal-Lobe Functions E.L. Highly organized botany college professor Became disorganized, showed little emotion, and began to miss deadlines Scores on intelligence and memory tests were superior Showed impairment on frontal lobe tests Infection in L frontal lobe Absence of facial expression 4 Divisions of Frontal Lobe Frontal lobe includes all the tissue anterior to the central sulcus. constituting 30% to 35% of the neocortex four general categories: primary motor, premotor, prefrontal, and anterior cingulate. 5 Primary Motor Cortex Specifies basic movements Controls movement force and direction Its cells project to subcortical motor structures such as the basal ganglia 6 1 5 Its cells project to subcortical motor structures such as the basal ganglia the red nucleus the spinal cord. 6 Premotor Cortex Immediately anterior to the motor cortex Selects and plans movements Can influence movement directly via the corticospinal tract or indirectly though projections to primary motor cortex 7 Premotor Cortex Contains FEF frontal eye fields Receive input from posterior parietal region PG & superior colliculus Can be divided into: Dorsal premotor cortex (PMd) Choosing movement from a movement lexicon Receive projections from parietal regions PE & PF Receive projections from DLPFC Ventral premotor cortex (PMv) Contains mirror neurons Receive projections from parietal regions PE & PF Receive projections from DLPFC Inferior frontal gyrus (Broca’s area) 8 Prefrontal Cortex PFC comprising the area anterior to the motor, premotor, and cingulate cortex Area of the prefrontal lobe that receives input from the dorsomedial nucleus of the thalamus PFC Receives significant input from the mesolimbic dopamine cells in the tegmentum Important role in regulating how prefrontal neurons react to stimuli including stress Contribute to emotional state 9 stimuli including stress Contribute to emotional state Abnormalities in theses projections à schizophrenia & drug addiction 9 PFC has 3 Regions in Primates: 1. Dorsolateral prefrontal cortex is interconnected with the posterior parietal cortex & superior temporal sulcus Connections with regions to which posterior parietal projects Cingulate cortex Basal ganglia Superior colliculus Its functions lies in its relationship to the PPC 2. Orbitofrontal cortex Gains input from all sensory modalities Main afferents from the temporal lobe, auditory regions of STG, visual regions of inferotemporal cortex TE, STS & subcortical amygdala Afferents from amygdala, S2, gustatory cortex in insula and olfactory regions of the pyriform cortex Projects to amygdala and hypothalamus >> route in which the OFC influences how the autonomic nervous system controls changes in blood pressure, respiration,.. 10 PFC has 3 Regions in Primates: 3. Ventromedial prefrontal cortex receives Receives cortical connections from the DLPFC, posterior cingulate cortex and medial temporal cortex Connects with amygdala and hypothalamus and periaqueductal gray in the brainstem Emotional behavior bodywide 11 Medial Frontal Cortex Research suggests there are three functional zones, each of which has multiple subregions 12 11 Research suggests there are three functional zones, each of which has multiple subregions Posterior zone serves motor functions Middle zone is involved with cognitive functions, pain, and affect Anterior zone is associated with the default mode network for reward, social processing, and episodic memory 12 Anterior Cingulate Cortex Cingulate cortex extends from the anterior of the corpus callosum to the posterior part of the corpus callosum Cingulate cortex is divided into the anterior (ACC), middle (MCC), and posterior (PCC) Dorsal ACC is involved in cognitive processes, is part of the default mode network, and is connected to the prefrontal cortex, PPC & FEF Ventral ACC is involved in emotional processes and is connected with the amygdala, nucleus accumbens, hypothalamus, hippocampus & A. insula 13 Frontal-Lobe Networks Regions of the frontal lobe are important in the default mode network, which seems most active when individuals have an internal focus Salience network involves the anterior cingulate cortex, supplementary motor area, and anterior insula and is important when there are important external stimuli requiring a behavioral change The shift in attention from internally directed thought to behavior guided by external events is accompanied by increased activity in the salience network and decreased activity in the default mode network. Dysfunction of the salience network leads to excessive activity in the default mode network and lapses in attention Prefrontal cortex, particularly the ventromedial cortex, is also important in networks involved in emotional behaviors 14 15 important in networks involved in emotional behaviors 14 Networks of the Frontal Lobe 15 Theory of Frontal-Lobe Function Patients with frontal-lobe lesions are challenged by talks involving Planning and selecting from multiple options Ignoring extraneous stimuli and attending to the task Keeping track of what has already been accomplished and what has yet to be done Sequential organization and implementing behavioral strategies in response to internal and external stimuli are functions of the frontal lobes 16 Functions of the Motor and Premotor Cortex Primary motor cortex executes basic movements Premotor cortex selects and coordinates sequences of movements Frontal eye fields direct the gaze toward specific targets or in response to internally generated goals The pairing between an external cue and a motor response is associated with increased activity in the premotor cortex 17 Functions of the Prefrontal Cortex (Part 1) Prefrontal cortex engages cognitive functions to select movements at appropriate times and locations Internal cues Temporal memory is the record of recent neural events and the order in which they occurred Temporal memory for motor (dorsal) and object information (ventral) likely stored in different parts of the prefrontal cortex, particularly the dorsolateral prefrontal cortex is esp engaged in selecting behavior based on temporal memory External cues If temporal memory is impaired, external cues become more important and patients have difficulty suppressing movements directed at external cues behavior is not under the control of internalized knowledge but is controlled directly by external cues Feedback about the rewarding nature of stimuli is an important 18 controlled directly by external cues Feedback about the rewarding nature of stimuli is an important external cue orbitofrontal cortex is central to learning by association. E.g., grandma & smell of cookies 18 Functions of the Prefrontal Cortex (Part 2) Context cues In social species, such as humans, context impacts behavior Sensory information from the temporal lobe is combined with affective information from the amygdala in the inferior frontal cortex Patients with damage to the orbitofrontal cortex have difficulty interpreting context and altering behavior appropriately- faux pas Autonoetic awareness your awareness of you and your timeline Self-knowledge or self-awareness Such awareness through memory enables us to understand our history and our future goals autonoetic awareness allows one to bind together the awareness of oneself as a continuous entity through time. Impairment in autonoetic awareness results in a deficit of behavioral self-regulation. Patients with medial or ventral frontal-lobe injuries lose this awareness 19 Heterogeneity of Frontal-Lobe Function Correlations among performances on tasks sensitive to frontal lobe injury are low Any individual patient is unlikely to show all the symptoms The severity of symptoms will vary with lesion location At least in the OFC, evidence of discrete localization of functions exists. depends on where the lesion is and how big the lesion is 20 OFC Much of the OFC is on the ventral surface of the brain 20 OFC Much of the OFC is on the ventral surface of the brain Stephen Frey and Michael Petrides –Examined functions of the orbital region using PET –Increased activity in area 13 to unpleasant auditory stimuli Has extensive connections with amygdala and hypothalamus –Increased activity in area 11 when learning new visual information Has connections with the ventral visual stream –Functional dissociation between the two areas Area 13: Responds to affective qualities Area 11: Processes new visual information 21 Executive Functions of Frontal-Lobe Networks Executive function is the ability to plan and generate new actions in response to changing environmental demands Attentional control Planning Reasoning Working memory Problem solving Abstract thinking Self-monitoring the frontal lobe is a big part but other exectuive functions also take part in this 22 23 Executive Functions These functions involve both the frontal lobes and other brain areas connected to the frontal lobes Dorsolateral frontoparietal network Interhemispheric dorsolateral frontal connections Fronto-striatal connections Executive functions are lateralized Left frontal lobe is important for setting tasks Right frontal lobe monitors ongoing tasks It is likely that there are multiple executive function networks Hot executive functions involve situations that are emotionally significant not to make descisions when you are emotional and sad Cool executive functions involve tasks that are emotionally significant Cool executive functions involve tasks that are emotionally neutral 23 Executive Function Various questionnaires have been developed to test specific behaviors and attitudes commonly associated with executive function, such as the Behavior Rating Inventory of Executive Function (BRIEF) the Frontal System Behavior Scale (FrSBe), a variety of tests related to everyday life, such as a multiple errands test Just because a patient does not show a deficit on certain tests of executive function does not mean the patient does not have an executive problem. Atypical development of the networks attention deficit/hyperactivity disorder neurodegenerative disorders frontal-lobe injury Skills associated with executive function appear to be important in supporting learning and school performance, where goal-directed problem solving and management of emotions are important. The predictive power of executive function tests is often greater than that of IQ in school performance 24 Symptoms of Frontal-Lobe Lesions 25 1. Disturbances of Motor Function Impairments of fine movements, speed, and strength following damage to primary motor cortex Difficulties in programming rapid sequences of skilled movements result from damage to the supplementary motor cortex, particularly for asynchronous movements of the left and right hands Patients with bilateral damage to the frontal lobes were significantly impaired at copying facial movements, especially the sequence of movements Control of voluntary eye movements is impaired following damage to the frontal lobes 26 to the frontal lobes 26 agramitism Motor Function and Frontal-Lobe Lesions If you shift your gaze, the visual world remains stable If you use your finger to move your eye, the objects around you appear to move Corollary discharge refers to the neural signal that indicates that a movement will occur, enabling the visual system to compensate for that movement and keep the world stable Cells in the frontal eye fields are involved in processing the corollary discharge information Broca’s area and the supplementary speech area are involved in selecting words based on internal and external stimuli Damage to these areas results in loss of grammar (agrammatism) or speech, Broca and supplementary respectively 27 28 most of these and tests have to do with convergent thinking (one right answer) 29 30 31 2. Loss of Divergent Thinking Damage to the frontal lobes does not result in consistent decreases in IQ, as opposed to damage to the parietal and temporal lobes Traditional IQ tests assess convergent thinking, where there is one correct answer Divergent thinking asks questions that are open-ended and do not have a single correct answer Frontal-lobe injuries interfere with divergent thinking more than convergent thinking Text Behavioral Spontaneity Patients with frontal-lobe damage are less spontaneous in their behaviors Produce fewer responses when asked to list words starting with a particular letter Fail to constrain the words they generate to the rules of the task, such as only listing words containing a certain number of letters Produce shaky script, suggesting motor containing a certain number of letters Produce shaky script, suggesting motor impairments Perseverate and repeat the same word scribble anything in the time span 30 Design Fluency 31 3. Environmental Control of Behavior Environmental cues and feedback are important to regulate behavior use environmtal cues to try and fix the behavior Patients with frontal-lobe damage struggle with using these cues Patients perseverate on a response and fail to shift strategy when the demands of the task change, such as the Wisconsin Card Sorting Task Cards vary in number of objects, shape of objects, and color of objects Participants sort cards into piles based on the objects on the cards, but are not told the rule, only whether they sorted correctly or incorrectly Once participants determine the correct rule, the experimenter changes the rule and participants need to inhibit the previous strategy and learn the new rule Patients with frontal-lobe damage continue to use the old rule, even if they know it is no longer correct 32 Wisconsin Card Sorting Task 33 Stroop Test: another test of response inhibition In this task, subjects are presented words, often color names, written in different colors of ink The task is to suppress the natural tendency to read the word, but instead to name to color of ink Task is difficult for neurotypical participants and almost impossible for patients with left-frontal-lobe lesions 34 Risk Taking and Rule Breaking Patients with frontal-lobe damage often fail to comply with instructions and take greater risks damge would be seen when it’s not as neat/creative and they run out of ideas 34 Patients with frontal-lobe damage often fail to comply with instructions and take greater risks Failed to alter behavior when a signal indicated they had made an incorrect turn in a maze Took greater risks and made more mistakes when trying to guess a word based on clues provided by the experimenter In an fMRI study of a gambling task in which the risks and rewards were ambiguous, there was increased activity in the orbitofrontal cortex and amygdala of control subjects in the condition where the risk was ambiguous the OFC is part of a neural decision-making circuit that evaluates degrees of uncertainty. 35 Self Regulation Patient’s autobiographic knowledge typically lost. Difficulty relating ot others Difficulties in regulating behavioral flexibility 36 Associative Learning Patients with frontal-lobe lesions fail to learn from experience Patients can describe what they are supposed to do, but fail to do it Participants learned that a particular color was associated with making a particular shape with their hand Participant memory was intact, but patients with frontal-lobe damage were unable to select the appropriate behavior from the possible responses 37 Poor Temporal Memory Delayed-response task is used to study memory in monkeys Chimpanzees watch as a reward is placed out of sight in front of them, such as in a recessed well or under a cup Chimp’s view of the scene is blocked for a period of time Chimp is allowed to view the scene and if they correctly identify where the reward is, they earn the reward Prefrontal damage reduces performance to the level of chance 38 Testing for Temporal Memory 39 38 Testing for Temporal Memory 39 Dorsolateral Prefrontal Cortex and Memory Monkeys trained to associate a tone with a color They then heard the tone and had to remember it for 10 seconds before responding A large contingent of DLPFC cells responded to one tone, and others to the other tone On incorrect trials, DLPFC cells did not respond 40 Studying Temporal Memory in Humans Test of recency memory in humans Participants are presented a series of cards that each have two items on them Stimuli can be pictures or words When there is a question mark between the cards, participants have to report which item they saw more recently Usually, both objects have been presented previously, but Text sometimes one object is novel When one object is novel, the judgement only requires recognition of the object seen before When neither object is novel, participants need to recall the order in which the objects were presented Frontal-lobe patients perform the same as controls on the recognition task, but are impaired when they need to recall the order of presentation 41 Impaired Social and Sexual Behavior Appropriate social and sexual behaviors require flexible responses depending on the context Frontal-lobe damage often results in significant changes in social behaviors and personality Phineas Gage was a railway worker who was injured by an iron rod passing through his prefrontal cortex as part of a workplace accident Personality changed significantly from responsible and familyand community-centered before the accident to irresponsible 42 43 Personality changed significantly from responsible and familyand community-centered before the accident to irresponsible and inpatient and capricious after the accident Damage was to Gage’s left frontal lobe 42 Frontal Injury Reconstruction Pseudodepression and Pseudopsychopathy Damage to orbitofrontal cortex results in more dramatic personality changes than damage to the dorsolateral prefrontal cortex Pseudodepression indifferent to emotional things and lack sexual interest Outward apathy and indifference Loss of initiative Reduced sexual interest Little overt emotion or verbal output Pseudopsychopathy the oposite Lack of tact or restraint and little social grace Coarse language Promiscuous sexual behavior Increased motor activity All elements of pseudodepression and pseudopsychopathy are observable only after bilateral frontal-lobe damage. Pseudodepression appears most likely to follow lesions of the left What are theses and where si the damge? frontal lobe, whereas pseudopsychopathic behavior seems likely to follow lesions of the right frontal lobe. 43 44 45 Deficits in Social and Sexual Behavior Anecdotal evidence suggests frontal-lobe damage alters libido and related behaviors, but social taboos have largely prevented empirical studies Damage to the orbitofrontal cortex reduces inhibitions, enabling abnormal sexual behavior, such as public masturbation Damage to dorsolateral prefrontal cortex reduce interest in sexual behavior- not a motor problem because can be guided step by step Removal of the frontal lobe of alpha male monkeys caused them to lose their position in the hierarchy Patients with orbitofrontal lesions might have difficulty understanding facial expressions. Patients with orbitofrontal lesions might have difficulty understanding facial expressions. 45 Does a Spatial Deficit Exist? Input to dorsolateral prefrontal cortex comes largely from parietotemporal regions involved in visuomotor guidance of movements Brain-imaging studies asking participants to navigate a familiar route show increases in blood flow in the dorsolateral prefrontal cortex Lesion studies of the frontal cortex show difficulty with memory tasks involving spatial locations Together, such studies suggest that the dorsolateral prefrontal cortex has some role in spatial memory and decision making 46 Neuropsychological Assessment Relatively few tests have been developed to assess the function of the frontal lobes On a battery of frontal-lobe tests, any individual is unlikely to do poorly on all of them, but a patient with frontal-lobe damage is unlikely to do well on all of them Wisconsin Card Sorting Task asks participants to shift strategies Word Fluency and Design Fluency tests ask subjects to produce as many words or abstract designs as possible in a specified time Tower of London and Tower of Hanoi ask subjects to move discs from one peg to another according to rules and are tests of planning Tests of spelling, aphasia, hand strength, and finger-tapping speed are also useful 47 Standardized Neuropsychological Tests 48 Intelligence and the Frontal Lobes The size of the prefrontal cortex has expanded rapidly in human evolutionary history, suggesting this region is related to human intelligence Yet, damage to the frontal lobes does not result in a decrease in intelligence Fluid intelligence involves seeing relationships and drawing logical conclusions 49 50 Fluid intelligence involves seeing relationships and drawing logical conclusions Crystalized intelligence is the ability to apply previous learning Fluid intelligence is associated with posterior parietal cortex and prefrontal cortex, which are connected by white-matter tracts 49 Brain Basis of Intelligence 50 Investigating Intelligence Researchers want to understand whether intelligence is the result of a single network within the parietal and frontal lobes or a collection of different specialized subsystems Brain-imaging studies support the involvement of multiple systems Multiple Demand Working Memory and Multiple Demand Reasoning were the most important two systems, together accounting for 90% of the participant variance on intelligence tests 51 Task-Related Activity During Cognitive Tests