Week 11 Flashcards
Frontal Cortex
• Posterior - motor areas • Anterior – association area – prefrontal cortex (PFC) • Important subregions • Lateral PFC (lPFC) dorsal and ventral portions (dlPFC, vlPFC) • Frontal pole (FP) • Orbitofrontal cortex (OFC) – ventromedial • Medial frontal cortex (MFC)
Prefrontal Cortex
• Massively connected – links motor, perceptual, and limbic • Large input from thalamus – connects PFC with BG, CB, brainstem nuclei • Almost all cortical and subcortical areas influence PFC either directly or by only a synapse or 2 • Many projections to contralateral hemisphere • Many connections bidirectional
Prefrontal Cortex – Sensory Input
Dorsal/ventral sensory divisions extend into PFC Dorsal - motor and executive control functions for which spatial information is important Ventral – mediate emotional responses to things in the environment – emotional significance first requires recognition
Prefrontal Cortex – Motor Contro
• Emotional and cognitive processes exert control over behaviour • Serial/functional hierarchy • vmPFC/OFC (emotional processes) to dlPFC (cognitive control) to motor
Prefrontal Cortex – Emotional
• vmPFC/OFC • Closely connected with limbic structures, especially amygdala • Influence cognition and directly influence ANS • Drives, motivation, valence, and the assessment of the emotional significance of sensory stimuli • Part of a system encoding emotions and emotional responses
Prefrontal Cortex
• PFC half of FL in humans • Human PFC expansion – more about white matter than grey matter • Connections! • PFC matures late in development • May not be fully developed until mid 20’s • Grey matter peaks earlier • White matter later • Connections!!!
PFC Myelination
• Higher cognitive functions for which the prefrontal cortex (language, intelligence, and reasoning) heavily rely on intracortical and corticocortical connectivity • Do not reach full maturity until mid 20’s • Corticocortical axons that develop most between childhood and adulthood are those that run from PFC to posterior association cortex • Those axons are part of the top–down frontal efferent pathways critically involved in cognitive control
Dysfunction - Phineas Gage
• 1848, Phineas Gage working as a foreman when an accident shot a steel rod through the front of his skull • Survived and reportedly got to his feet and walked away • “I did not believe Mr. Gage's statement at that time ... Mr. Gage persisted in saying that the bar went through his head ... He got up and vomited; the effort of vomiting pressed out about half a teacupful of the brain [through the exit hole at the top of the skull], which fell upon the floor • Significant part of his left frontal lobe destroyed • Dramatic personality shift but memory and general intelligence seemed unimpaired after the accident • “most efficient and capable foreman ... a shrewd, smart business man, very energetic and persistent in executing all his plans of operation” • Social problems - now fitful, irreverent, and grossly profane, showing little deference for his fellows. • He was also impatient and obstinate, yet capricious and vacillating, unable to settle on any of the plans he devised for future action. • His friends said he was “no longer Gage." • Most serious mental changes were temporary • Became far more functional, and socially far better adapted • A social recovery hypothesis suggests that Gage's work as a stagecoach driver in Chile fostered this recovery by providing daily structure which allowed him to regain lost social and personal skills. • 1860, he began to have epileptic seizures and died a few months later
Dysfunction - Frontal Lobotomy
• Treatment of psychiatric disorders 1930’s to 1950’s (pre drugs) • Moniz pioneered based on reported effects of frontal lobectomy in chimps (won Nobel in 1949) • Isolate PFC rather than remove
Frontal Lobotomy
Transorbital sectioning • Electroshock anaesthesia • Icepick tapped through top of the orbit • Insert 5cm into brain and “wiggle” Leucotome • Insert 6 times with cutting wire retracted • Extrude cutting wire and rotate • Cut out a core of tissue • Anecdotal reports – patients were ‘stimulus-bound’: • Reacted to whatever was in front of them and did not respond to imaginary situations, rules, or plans for the future. • Some gained significant weight, and / or became sexually promiscuous • Could not form / sustain goals • Distracted by circumstances
Dysfunction - Frontal Astrocytoma
• Patient W.R - the man who had “lost his ego”
• Life changed after he earned his law degree - over 10
years from graduation:
• Had not taken the bar exam 4 years after graduation, or
even looked for a job
• No motivation
• Worked as instructor in a tennis club
• Family described him as ‘drifting’
• Poor state financially, borrowing from brother
• Eventually gave up tennis: became demotivated and
nonchalant during matches, not keeping score
• Lost interest in romantic pursuits
Frontal Astrocytoma
• Suffered a seizure in his last year of college
• No identifiable cause (on PET or CT) at the time
• CT re-done:
• extremely large astrocytoma
• Traversing along the callosal fibres, invading
extensively the lateral prefrontal cortex in the left
hemisphere, and considerably in the right
• Poor prognosis: death within ~1 year
• Response of W.R.: passive, detached, no rage,
minimal anguish, general absence of concern
Dysfunction - FTD
• Frontotemporal dementia or “Pick’s Disease”
• In 1892, Arnold Pick described a man who had
presented in life with progressive loss of speech
and dementia.
• When the patient died his brain was found to be
atrophied.
• This shrinkage had been caused by brain cells dying
in localized areas.
• This feature of localization is very different to
Alzheimer’s disease where the atrophy is more
generalized.
Frontotemporal Dementia (FTD)
Atrophy of frontal lobes and anterior temporal lobes ‘knife-edging’ – thinning of the gyri from neurodegeneration Atrophy with ventricular dilation Swollen neurons with abnormal tau protein inclusions
Frontotemporal Dementia (FTD)
Abnormal spontaneous behaviours during examination
• Inappropriate jocularity
• Echolalia (repeating the examiner’s words), echopraxia
(repeating the examiner’s gestures)
• Disinhibited approach or utilization behaviours
• Unkempt, depressed in early stages
During the first 2 years - “classic” frontal lobe syndromes:
• orbitofrontal dysfunction: aggressive and social
inappropriateness (may steal or demonstrate obsessive or
repetitive stereotyped behaviours), apathy and disinhibition
• dorsomedial or dorsolateral dysfunction: lack of concern,
apathy, or decreased spontaneity.
Speech and language
• Abnormalities often begin early and progress fast
• Memory impairment relatively less severe than
speech/language and behavioural changes
• Verbal output that is often nonfluent, with poor naming
of objects
Movement disorders
• Akinesia, plastic rigidity, or paratonia (involuntary
resistance) on motor examination
Perseveration
