Published on March 9, 2014
FRONTAL LOBE: ANATOMY & CLINICAL RELEVANCE IMRAN RIZVI
Anatomy • The frontal lobes lie anterior to the central or rolandic sulcus and superior to the sylvian fissure. • It makes up about the anterior one-half of each hemisphere in man. • They are larger in humans than in any other primate .
Sulci and Gyri • On the lateral aspect of frontal lobe 3 sulci are visible: • • • • precentral sulci, superior frontal sulci and inferior frontal sulci. In between these sulci are 4 gyri: precentral gyrus between central and precentral sulcus. Superior frontal gyrus: superior to superior frontal sulcus. Middle frontal gyrus: between superior and inferior frontal sulcus. Inferior frontal gyrus: inferior to inferior frontal sulcus.
• On the medial surface, the frontal lobe extends down to the cingulate sulcus. • The paracentral lobule consists of the extensions of the precentral and postcentral gyri onto the medial hemispheric surface above the cingulate sulcus; it is important in bladder control. • The inferior frontal gyrus is divided into the pars orbitalis, pars triangularis, and the pars opercularis. • On the inferior surface lies the olfactory sulcus, olfactory bulb and tract overlies this sulcus.
Orbital surface Frontal lobe • Divided into four orbital gyri by M L a well-marked H-shaped orbital sulcus. • The medial, anterior, lateral, and posterior orbital gyri. • The medial orbital gyrus presents a well-marked antero-posterior sulcus, the olfactory sulcus, for the olfactory tract; • the portion medial to this is named the gyrus rectus
Functional Frontal Lobe Anatomy Clinically important areas of the frontal lobe include •The primary motor area. •The premotor Area. •Supplementary motor areas. •The prefrontal region. •The frontal eye fields. •The motor speech areas.
Primary motor cortex • Primary motor area, or Brodmann area 4, occupies the precentral gyrus extending over the superior border into the paracentral lobule. • The primary motor area, if electrically stimulated, produces isolated movements on the opposite side of the body as well as contraction of muscle groups concerned with the performance of a specific movement. • The movement areas of the body are represented in inverted form in the precentral gyrus
Primary motor cortex • Input: Thalamus, Basal ganglia, sensory, premotor areas • Output: Motor fibers to brainstem and spinal cord • Function: Executes design into movement.
Pre motor area • The premotor area (Area 6), is wider superiorly than below and narrows down to be confined to the anterior part of the precentral gyrus. • It has no giant pyramidal cells of Betz. • Electrical stimulation of the premotor area produces muscular movements similar to those obtained by stimulation of the primary motor area; however, stronger stimulation is necessary to produce the same degree of movement.
Pre motor cortex • Input: Thalamus, Basal ganglia, sensory cortex • Output: Primary motor cortex • Function: sensorimotor integration, stores motor programs • Lesions: Inability to make use of sensory feedback in performance of smooth movements and apraxia
Supplementary motor area • The supplementary motor area ( area 6) is situated in the medial frontal gyrus on the medial surface of the hemisphere and anterior to the paracentral lobule. • Stimulation of this area results in movements of the contralateral limbs, but a stronger stimulus is necessary than when the primary motor area is stimulated.
Supplementary motor area • Input: Cingulate gyrus, Thalamus, sensory & prefrontal cortex • Output: Premotor, primary motor cortex • Function: procedural Intentional memory: preparation recall of for movement; memorized motor sequences • Lesions: Mutism, contralateral motor neglect, impairment of bi brachial coordination.
Frontal eye field • It is Broadmann area 8. • It is located in the middle frontal gyrus. • Input: Parietal / temporal (what is target & where is target) • Output: caudate; superior colliculus; paramedian pontine reticular formation • Function: it is considered to control voluntary scanning movements of the eye. • Lesion: Eyes deviate ipsilaterally with destructive lesion and contralaterally with irritating lesions.
Broca’s speech area • Brodmann area 44 • It is located in the inferior frontal gyrus. • In the majority of individuals, this area lies on the left or • • • • dominant hemisphere. Input: Wernicke’s area Output: primary motor cortex Function: speech production (dominant hemisphere); emotional, melodic component of speech (non-dominant) Lesions: motor aphasia.
Pre frontal area • The most anterior parts of the frontal lobes (areas 9 to 12 and 45 to 47), sometimes referred to as the prefrontal areas, are particularly well developed in human beings. • Is also called as organ of civilization. • These areas are connected with the somesthetic, visual, auditory, and other cortical areas by long association bundles, and with the thalamus and the hypothalamus by projection fibers. • Clinically, the prefrontal region can be divided into the dorsolateral prefrontal cortex (DLPFC), the medial prefrontal cortex (MPC), and the orbitofrontal cortex (OFC).
•The Case of Phineas Gage (Harlow 1848) Tamping iron blown through skull: L frontal brain injury Excellent physical recovery Dramatic personality change: ‘no longer Gage’: stubborn, lacked in consideration for others, had profane speech, failed to execute his plans, became erratic
DLPFC • The DLPFC is important in the organization of self• • • • ordered tasks. It plays a critical role in the neural network subserving working memory . The responsibility for executive function largely resides with the DLPFC and its connections. Frontal lobe executive function is the ability to plan, carry out, and monitor a series of actions intended to accomplish a goal. Lesions: executive function deficit; disinterest apathy, decresed attention to relevant stimuli.
OFC and MPC • The OFC has important connections with the limbic system, including the amygdala. • Disinhibition syndromes, ranging from mildly inappropriate social behavior to full-blown mania, may occur with dysfunction of the OFC, particularly of the right hemisphere. • Lesion of MPC causes Paucity of spontaneous movements, sparse verbal output, lower extremity weakness and incontinence.
Vascular supply • Medial parts of frontal lobe: Anterior cerebral artery • Convexity and deep regions: Superior (rolandic) division of MCA • Underlying deep white matter: series of small penetrating arteries (lenticulostriate) directly from stem of MCA
Frontal subcortical circuits • The connections of the frontal lobes were described in details by Goldman Rakic. • Five FSCs have been described: 1.Motor 2.Oculomotor 3.Dorsolateral prefrontal 4.Lateral orbitofrontal 5.Anterior cingulate
• These circuits share a general structure consisting of the cortex, basal ganglia and thalamus. • Information originates from the cerebral cortex, travels first to the basal ganglia then on to the thalamus, and finally returns to numerous areas of the cortex. • All FSC circuits have both a direct and an indirect pathway, which have “opposite” or reciprocal functions.
Direct FSC • The basal ganglia can be characterized as either “input” or “output” nuclei. • The caudate, putamen, and ventral striatum make up the input nuclei and receive excitatory glutamate projections from multiple areas of the cortex. • The input nuclei then connect by way of inhibitory GABA fibers to the major output nuclei, which consist of the internal segment of the globus pallidus and the pars reticulata of the substantia nigra. • The output nuclei send inhibitory GABA efferents to thalamic nuclei that project back to the cortex by way of excitatory glutamate fibers.
Indirect FSC pathway • The indirect pathway tends to inhibit the thalamus and decreases excitatory drive to the cortex. • This circuit involves GABA projections, first from the striatum to the globus pallidus externa, then on to the subthalamic nucleus. • Projections then connect with the globus pallidus interna and substantia nigra by way of glutamate neurons. • This reciprocity of the direct versus indirect pathways is believed be involved in the initiation and cessation of behaviors required for adaptive functioning.
FSC: Motor circuit • • Supplementary Motor & Premotor: Planning, initiation & storage of motor programs; fine-tuning of movements Motor: final station for execution of the movement according to the design
FSC: Oculomotor circuit •Voluntary scanning eye movement
FSC: Dorso-lateral circuit Lateral Prefrontal DL Caudate DM Globus Pallidus Substantia Nigra VA, MD Thalamus This circuit is responsible for executive functions. •motor planning, deciding which stimuli to attend to, shifting cognitive sets •Attention span and working memory •Lesion: difficulty focusing and sustaining attention as well as reduced verbal fluency and motor programming
FSC: Orbito-frontal circuit Infero-lateral prefrontal Orbito-frontal • This VM Caudate DM Globus Pallidus Substantia Nigra VA, MD Thalamus circuit mediates empathic, civil and appropriate behavior. • Lesion: Disinhibition and emotional liability. socially
FSC: Anterior Cingulate Circuit Anterior Cingulate Gyrus Ventral Striatum RL Globus Pallidus Substantia Nigra • This circuit is involved in motivational mechanisms. • Lesions: Abulia, akinetic mutism.
Frontal lobe: Neuro-imaging • The central sulcus is a useful landmark for identifying frontal lobe. • But identifying it with certainty can present some difficulty on CT and MR images. • On axial scans, follow the superior frontal sulcus from anterior to posterior until it meets and forms an angle with the precentral sulcus – the central sulcus is the next one behind. • On lateral sagittal images note the Y-shaped sulcus of the pars triangularis at the anterior end of the Sylvian fissure. The next major fissure posterior to the Y is the precentral sulcus
• On medial sagittal images follow the cingulate sulcus as it ascends superiorly and posteriorly towards the vertex as the pars marginalis, the central sulcus lies just in front of pars marginalis. • The precentral gyrus contains an area at its superior lateral part, which resembles an upside-down omega, an area of cortex that represents the motor-hand area.
Frontal lobe syndromes Three Frontal Lobe syndromes •Orbitofrontal syndrome (lacks inhibition) •Frontal Convexity syndrome (apathetic) •Medial Frontal syndrome (akinetic)
Orbito-frontal syndrome • Characterized by disinhibited, impulsive behavior, difficulty in controlling their emotions, lacking in judgment and are easily distracted • Many patients are incorrectly diagnosed with a personality disorder
Frontal Convexity syndrome • Characterized by disinterest, slowing of the motor functions and apathy. • Inability to regulate behavior according to personal goals. • Inability to plan ahead, lack of motivation and concern. • Generally not caring about the world around them.
Medial Frontal syndrome • Characterized by mutism and akinesia. • profound apathy, motor and verbal inactivity and indifference to thirst or hunger. • Loss of sensation and weakness of lower extremities along with urinary incontinence.
Right and left functional lobes lesional Deficits
Clinical Assessment of frontal lobe • History, Examination and formal tests : Abnormal behavior, speech disorder, urinary incontinence, Frontal gait(magnetic gait) , weakness of limbs • Test sense of smell. • Frontal release reflexes Grasp reflex Sucking reflex (pout, snout, rooting) Palmo-mental reflex Glabellar tap reflex
Clinical assessment contd.. To assess the following functions: • Emotional make-up and personality • Abstraction and judgment • Attention and memory • Language
Emotional make-up and personality is best assessed by history from family / friends & observation. •Abstraction and judgment are assessed by proverb interpretation and similarities. •E.g explain in your own words the meaning of •Don’t cry over spilled milk •Rome was not built in a day. •Similarity between mango and orange, turnip and cauliflower, car and airplane.
Attention and memory • Attention is the patient’s ability to attend to a specific stimulus without being distracted by external, internal or environmental stimuli. • Attention can be tested by alternative sequence MNMN) • Luria’s ‘fist-edge-palm’ test • Go/no-go: ”tap once if I tap twice, don’t tap if I tap once” “tap for A” read 60 letters at 1/sec (e.g. copying
Digit span test: Measure of short term memory •“repeat 3-5; 7-5-8; 3-9-4-8..” N: >5 •A two year child has a digit span of 2, 3yr- 3, 4yr- 4, 5yr- 5, 6yr-6 and 7yr to adult- 7
Language • Handedness • Spontaneous speech • Comprehension • Naming • Repetition • Reading and writing.
Formal Tests • Wisconsin Card Sorting Test • Trail Making • Stroop Color & Word Test
Wisconsin Card Sorting Test • Used primarily to assess perseveration and abstract thinking. • The WCST is also considered a measure of executive function because of its reported sensitivity to frontal lobe dysfunction. • The WCST consists of four key cards and 128 response cards. • The task requires subjects to find the correct classification principle by trial and error and examiner feedback.
Trail Making Test • Test for visual attention and task switching. • Trail Making Test consist of 25 circles distributed over a sheet of paper. • In Part A, the circles are numbered 1 – 25, and the patient should draw lines to connect the numbers in ascending order. • In Part B, the circles include both numbers (1 – 13) and letters (A – L); as in Part A, the patient draws lines to connect the circles in an ascending pattern, but with the added task of alternating between the numbers and letters (i.e., 1-A-2-B-3-C, etc.).
Trail Making Test 5 A B 4 6 1 C 2 D 3 7
Trail making test results
Test for perseveration
A frontal assessment battery at bedside: FAB • Similarities (conceptualization) • Lexical fluency (mental flexibility) • Motor series “Luria” test (programming) • Conflicting instructions (sensitivity to interference) • Go–No Go (inhibitory control) • Prehension behaviour (environmental autonomy)
Similarities (conceptualization) “In what way are they alike?” •A banana and an orange •A table and a chair •A tulip, a rose and a daisy •Score (only category responses [fruits, furniture, flowers] are considered correct) •Three correct: 3 Two correct: 2 One correct: 1 None correct: 0
Lexical fluency (mental flexibility) • “Say as many words as you can beginning with the letter S any words except surnames or proper nouns.” • The time allowed is 60 seconds. • Score (word repetitions or variations [shoe, shoemaker], surnames, or proper nouns are not counted as correct responses) • > 9 words: 3, 6 -9 words: 2, 3 -5 words: 1, < 3 words: 0
Motor series “Luria” test The examiner, seated in front of the patient, performs alone three times with his left hand the series of fist,edge,palm. •Now, with your right hand do the same series, first with me, then alone. •The examiner performs the series three times with the patient, then says to him/her:Now, do it on your own. •Patient performs six correct consecutive series alone: 3 •Patient performs at least three correct consecutive series alone: 2 •Patient fails alone, but performs three correct consecutive series with the examiner: 1 •Patient cannot perform three correct consecutive series even with the examiner: 0
Conflicting instructions • Tap twice when I tap once. • To ensure that the patient has understood the instruction, • • • • a series of 3 trials is run: 1-1-1. Tap once when I tap twice. To ensure that the patient has understood the instruction, a series of 3 trials is run: 2-2-2. The examiner then performs the following series: 1-1-2-12-2-2-1-1-2. Score No errors: 3, 1 -2 errors: 2, > 2 errors: 1
Go–No Go • “Tap once when I tap once.” • “Do not tap when I tap twice.” • Score No errors: 3, 1 -2 errors: 2, > 2 errors: 1 • Patient taps like the examiner at least four consecutive times: 0
Prehension behaviour • “Do not take my hands.” • The examiner is seated in front of the patient. Place the patient’s hands palm up on his knees. • Without saying anything or looking at the patient, the examiner brings his own hands close to the patient’s hands and touches the palms of both the patient’s hands, to see if he will spontaneously take them. • Patient does not take the examiner’s hands: 3 • Patient hesitates and asks what he/she has to do: 2 • Patient takes the hands without hesitation: 1 • Patient takes the examiner’s hand even after he/she has been told not to do so: 0
Interpreting results • A cut off score of 12 on the FAB has a sensitivity of 77% and specificity of 87% in differentiating between frontal dysexecutive type dementias and AD.
Conclusion • Frontal lobes besides controlling motor, oculomotor and • • • • language functions also allow the organism to learn from experience, and organize current information and choose a course of action, to summon drive to execute the action, and remain attentive and resist distraction. Lesion of DLPFC or its circuits causes loss of executive functions. Orbito-frontal/circuits: Disinhibition Anterior cingulate circuit: Abulia Frontal Assessment battery is a useful bedside test to differentiate frontal lobe syndromes with other causes of dementia.
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