Frontal lobe- anatomy, physiology, functions and clinical aspects

Frontal lobe its anatomy and functions, the important pathways and clinical aspects

1. Frontal lobe In psychiatry. DR.SARANYA.S

2. evolution Most recently evolved. Well developed only in primates Frontal lobe of earliest primates were under selective pressure to identify and eat fruits with their forelimbs. The brain of hominins may have exapted these region for manipulation, toolmaking, eventually language.

3. INTRODUCTION Impressively developed in humans and make up more than 1/3 rd of entire cortex. Caudally – motor cortex controlling the actions of our body More rostrally – prefrontal cortex mediating highest cognitive and behavioral functions.

4. neuroanatomy Lies anterior to central sulcus with three anatomical distinct regions ; dorsolateral, medial, orbital. Motor makes up the posterior portion of dorsolateral and medial region. Prefrontal cortex is everything that is anterior to motor area.

5. Frontal lobe

6. Functional divisions Motor cortex (MC) Primary MC Premotor Cortex Supplementary MC Frontal eye field Broca’s speech area Corticospinal and Corticobulbar origin. Prefrontal cortex (PFC) Dorsolateral PFC Ventrolateral PFC Dorsomedial PFC Ventromedial PFC Anterior cingulate Cortex Orbitofrontal Cortex Served by axons from mediodorsal thalamic nucleus

7. Motor cortex

8. Primary mc BA 4. About one third of pyramidal tract arise from here and the control exerted is greatest over the musculature of hand. ( distal limb musculature) The axons also terminate in basal ganglia, reticular formation, red nucleus and cranial motor nuclei.

9. Lesion  Paralysis of contralateral musculature. Initial flaccidity, later spasticity. Gross movement reappears but fine movements are often lost permanently.

10. Premotor cortex BA 6. 30% of pyramidal tract originates from here. ( proximal limb musculature) Receive input from superior parietal cortex and the axons leave and terminate in primary MC.

11. Others descend from premotor area through internal capsule to the reticular formation. (body posture and locomotion) Functions : motor learning, initiation and planning of actions.

12. Lesion  moderate weakness of contralateral shoulder and pelvic muscle  impairment in visually guided movements.

13. Mirror neurons 1st observed in premotor cortex of monkeys. Watching a movement and then doing the same  same neurons are fired; logically related actions. In humans, these are in primary MC, supplementary MC, primary somatosensory area and the inferior parietal cortex.

14. Supplementary mc Pre SMC Supplementary Eye Field- ocular motor extension SMA SMC proper

15. Afferent from primary somesthetic area of parietal lobe, superior parietal lobule, PFC and the cingulate gyrus. Efferent to the premotor and primary MC, connections with basal ganglia projecting to red nucleus and spinal cord. Functions : complex motor coordination, preparation for intentional movement and the procedural memory .

16. Lesion  motor neglect  u/l: Difficulty in complex motor routine for speech and ideomotor limb apraxia. severe, b/l: Akinetic mutism

17. Frontal eye field BA8. Projects to superior colliculus, to caudate nucleus, to parapontine reticular formation (lateral gaze) and to midbrain. Functions : voluntary eye movements and saccadic eye movements.

18. Lesion  deviation of ipsilateral eye with destructive lesion and deviation of contralateral eye in irritating lesion.

19. Broca’s area Speech production and the major input is from Wernicke’s through arcuate fasciculus. Project to primary MC controlling facial muscles.

20. Prefrontal cortex (pfc)

21. Permits high levels of complex cognition and socio behavioral processing.

22. dlpfc Extends between the longitudinal cerebral fissure above and lateral fissure below on lateral surface of brain. Lesion  executive function deficits; reduced emotional reactivity or disinterest and impaired goal oriented behavior.

23. DLPFC Inputs : motor cortex and temporoparietal junction. Evaluate information from somatosensory system. Monitors and adjust behavior using 'working memory.’

24. DLPFC

25. DLPFC

26. DMPFC BA 8, BA9, BA10 and some portion of BA 32 on the medial aspect of PFC. Major connections are with the cingulate gyrus, hippocampal formation and superior temporal gyrus.

27. Function : Engage in introspection Motivation and initiation of activity Evaluate emotional aspects of gaze Involved in emotional processing Activated by theory of mind tasks Lesion  apathy, lack of spontaneity and failure to respond, incontinence.

28. VLPFC BA 44, BA 45 and the lateral aspect of BA 47. Pars opercularis ,pars triangularis, pars orbitalis and Broca's speech area Left VLPFC involved in semantic processing Right VLPFC in emotional regulation.

29. vmpfc Located inferior to DMPFC BA10,BA12,BA32 Inputs : all sensory modalities. Connections with the ACC, anterior insula, amygdala, and nucleus accumbens.

30. VMPFC Important guide to decision making. Social brain.

31. Function is to identify valence and emotional tone of both interoceptive and exteroceptive stimuli.

32. Orbitofrontal cortex Ventral surface of frontal lobe from gyrus rectus to ventrolateral convexity laterally Limen insulae posteriorly to frontal pole BA11, BA12, BA47 Input: temporal association cortex, amygdala and hypothalamus (emotional processing). Also from visual system, taste, olfaction and somatosensory regions.

33. ORBITOFRONTAL Medial OFC activated during anticipation of reward. Lateral OFC activated during absence of reward.

34. Lesion  disinhibition, distractibility, hyperactivity, emotional lability.

35. ‘ The vmpfc +b/l temporoparietal.’ An important component of social brain. ; unique capability to mentalize, or make inferences regarding others thoughts, beliefs, and feelings- empathy; the highest form of knowledge. THEORY OF MIND

36. ANTERIOR CINGULATE CORTEX Evaluate incoming emotion provoking stimuli and help to decide the most appropriate response . Output: autonomic control centers, ; hypothalamus, and certain brainstem nuclei including periaqueductal gray.

37. Frontal subcortical Circuits : 1. 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. SMA, Premotor, Motor Putamen VL Globus Pallidus VL, VA, CM Thalamus Hypo-thalamus

38. 2. Oculo motor Circuit Voluntary scanning eye movement Independent of visual stimuli Frontal Eye Field Central Caudate DM Globus Pallidus Substantia Nigra VA, MD Thalamus

39. 3. Dorsolateral Prefrontal Circuit Lateral Prefrontal Caudate DL Executive functions: motor planning, deciding which stimuli to attend to, shifting cognitive sets Attention span and working memory DM Globus Pallidus Substantia Nigra VA, MD Thalamus

40. 4. Lateral Orbitofrontal Circuit Emotional life and personality structure Arousal, motivation, affect Orbitofrontal cortex: consciousness VM Caudate DM Globus Pallidus Substantia Nigra VA, MD Thalamus Infero-lateral prefrontal Orbito-frontal

41. 5. Anterior Cingulate Circuit Abulia , akinetic mutism Anterior Cingulate Gyrus Ventral Striatum RL Globus Pallidus Substantia Nigra MD Thalamus

42. Prefrontal lobe syndrome

43. Dorsal convexity dysexecutive syndrome Deficits in cognitive flexibility, temporal ordering of recent events, planning Results in reduced state of mental control, perseveration, impairment of sustained attention Diminished judgement ,impaired working memory, insight and selfcare Stimulus bound behavior.

44. Disinhibitory syndrome of orbitofrontal cortex Socially inappropriate behavior Inappropriate sexual act Aggression or criminal behavior Loss of manners or decorum Poor hygiene Lack of etiquette Impulsive rash and careless actions New onset gambling Reckless driving

45. Apathetic syndrome of medial frontal lobe Lack of initiative and reduced motivation Ceasing to engage in activities Social isolation Need prompting to intiate Doesn’t sustain conversation

46. Involvement of frontal lobe IN neuro psychiatry

47. The Case of Phineas Gage ( Harlow 1868 ) Penetrating iron rod blown through skull excellent physical recovery dramatic personality change: ‘no longer Gage’: stubborn, lacked in consideration for others, had profane speech, failed to execute his plans

48. Increased activity in DMPFC and Post cingulate gyrus ------- positive symptoms. Reduced frontal activity, increased volume loss in the ACC and medial OFC ------ negative symptoms. Schizophrenia( funct )

49. Schizophrenia (hist) Increase in number of axospinous synapses Decrease in axodendritic synapses Gray mater reduction .

50. Increased dopamine release in striatum, reduced density of D1 like dopamine receptors including D1 and D5.-------Cognitive deficiencies, poor working memory. Increased number of D2 like receptors including D2,D3,D4 ------ Positive symptoms. Schizophrenia

51. depression Common in patients with lesion in anterior left PFC and disorders of frontal executive dysfunction. Imaging studies revealed reduced metabolism in left PFC( DLPFC ) in active major depression.

52. depression Other studies indicate depression related cognitive deficits and withdrawal ---reduced blood flow to DMPFC or intrinsic networks within PFC. Unmedicated depressive cases  abnormal increase in activity of OFC, VLPFC and ACC as well as limbic areas. Also reduction noted with use of antidepressants.

53. BPAD Depressed BPAD patients showed decreased metabolism in DLPFC and limbic areas, especially in left and in subgenual ACC. Also reduced gray mater volume and glia.

54. BPAD In mania---reduction in activity in the right OFC, as well as increased activity in amygdala. Reduced volume of tracts in OFC  impulsivity or unstable mood.

55. OCD Reduced volume and increase in grey matter density in left OFC. Increased metabolism in OFC with whole cerebral hemispheres, caudate nuclei, and bilateral ACC.

56. Autism spectrum disorder Impaired theory of mind Include atypical activity in MPFC, posterior cingulate gyrus. Working memory associated with DLPFC, may also be impaired. May also involve OFClimbic circuitory But no absence of mirror neuron system.

57. Border line personality disorder Reduced metabolism and volume reduction in OFC, prefrontal cortex as well as hippocampus and amygdala Reduced volume correlate with impulsivity and aggressive behavior .

58. FTD Degenerative changes in the anterior temporal and posterior frontal areas. 3 variants: - semantic non fluent aphasia ( bv ) behavioral. FTD ( bv ) manifests frontal lobe syndrome, pathology localized to medial frontal and anterior temporal; VMPFC, ACC and OFC.

59. pTSD Hyperarousal PTSD response to traumatic narratives with increased autonomic and emotional responses --- decreased activity VMPFC and ACC. Dissociated PTSD --- increased activity in the VMPFC and ACC.

60. Frontal Lobe tests 1. Test of planning Tower of London test Measures the ability to plan.

61. Stroop Color and Word Tests RED BLUE ORANGE YELLOW GREEN RED PURPLE RED GREEN YELLOW BLUE RED YELLOW ORANGE RED GREEN BLUE GREEN PURPLE RED 2.Tests of response inhibition. Measures selective attention and to solve response conflict.

62. Go-no-go test of luria Raise one finger on tap of one, two finger on tap of two

63. Trail Making Test A C 1 2 7 3 D 5 B 4 6 Various levels of difficulty: 1. “Please connect the letters in alphabetical order as fast as you can.” 2. “Repeat, as in ‘1’ but alternate with numbers in increasing order” 3. Test of mental flexibility

64. Wisconsin's card sorting test Measures mental flexibility and the ability to shift cognitive sets.

65. 4.Test of fluency : ability to generate information within a fixed period. Word fluency- FAS test: in 1 min(nl-36-60) LEFT L/N Semantic fluency: 1 min(nl-18-22)  RIGHT L/N Design fluency: As many designs possible in fixed time

66. 5. Test of sequencing Graphic sequencing: Motor sequencing: FIST-EDGE-PALM, FIST-RING Conceptual series completion: 1,3,5,…

67. 6. Abstract thinking Proverb interpretation : one with frontal lobe lesion is unable to connect literal and metaphorical meanings of proverb.

68. 7.Attention and concentration Tap ‘A’ test Random letter cancellation test (attention, visual search and mental speed) 1 min

69. 8. Working memory Digit backward test Letter number span test : provide random numbers or letters, ask to repeat in ascending order.

70. 9. Tests of intentional motor system Motor impersistence : ask to close the eyes for 20 secs. Ask to hold arm stretched for 20 secs Motor perseveration: ask to draw double loop or cancel a target number or letter Echopraxia: ask to show two finger when examiner show one or not ton put any.

71. 10. LANGUAGE- Spontaneous speech Comprehension Naming Repetition- single words, phrases. Reading Reading and obeying

72. Thank you