THE FRONTAL LOBE

v

FLFunction: It is the end point for the visuomotor and object-recognition functions. The frontal lobe selects behaviors withrespect to context and internalized knowledge.

Separated from the parietal lobeby the central fissure and from the Temporal lobe by the SylvianFissure.Constitutes 20% of allthe neocortex.

FL

a)Lateral area 6: premotor cortex (plus Broca’s area, 44) b) Medial area 6: supplementary motor cx c)Area 8: Frontal eye field d) Area 8A: supplementary eye field

Subdivisions of the FL

3 general zones:1. Motor (area 4)2. Premotor (areas 6 & 8)

3. Prefrontal: a) Dorsolateral (9, 46)b) Inferior (11, 12, 13, 14) alsocalled orbital frontalc) Medial frontal (25, 32)

FLConnections

1. The motor cortex projects to the spinal cord, basal ganglia and brainstem. Involved in the control of movement.

2. The premotor cortex projects to the motor cortex, receives projections from PE and PF and dorsolateral preforntal. Influences movement.

2.1 Areas 8 and 8A send and receive projections from PG and superiorcolliculus to control eye movement.

FLConnections cont…

The prefrontal areas are the end points of the dorsal and ventral streams1. Dorsolateral prefrontal (9, 46) receives inputs from the PP areas

and the STS (reciprocal connections). Connections to cingulatecortex, basal ganglia and superior colliculus.

DA projections form the basal gangliaAnd the ventral tegmentum

FLConnections cont…2. The orbito frontal cortex (11-14) receives inputs form the temporal lobe (TE, STS) and the amygdala. Also connections from gustatory cortex, somatosensory and olfactory. OF cortex gains input from all sensory modalities.

FLTheory of F.L Function

(Dinner story)•Planning in advance and selecting form many options•Ignoring extraneous stimuli and persisting in the task at hand•Keeping track of what you have done.

Temporal organization of behavior

Motor and Premotor CortexThe motor cortex: executes movement

The premotor cortex: selects movements depending on external and internal cues.

The lateral area 6 is responsible for behavior in response to external cues.

The medial area 6 on the basis of internal knowledge. (Dog story)

FLTheory of F.L Function cont…

Prefrontal CortexControls cognitive processes necessary to make the movements at correct time and place. Could be controlled by internal or external orit may be made in response to context or self-knowledge.

A) Internal: Temporal memory, neural record of recent events, also called working memory or short term memory.

B) External: Events, circumstances happening while performing abehavior. E.g. shoe store on your way to buy milk.

C) Context: Multiple simultaneous roles, rules of behavior. E.g. howto act with your friends vs. your grandma

D) Autonoetic Awareness: awareness of yourself as a continuous entity over time. Autobiographical memory

FLFrontal Lobe Symptoms

1. Motor disturbance2. Loss of divergent thinking3. Environmental control4. Poor temporal memory5. Impaired social & sexual

behavior6. Olfaction deficits7. Face symptoms

FLMotor symptoms

•Inability to make fine movements•Loss of speed and strength•Deficits in programming movements (series of movements in a row)•Deficits in voluntary gaze movements•Deficits in corollary discharge. When the eyes move there is a neural signal that movement will happen and the world stays still. The frontal cortex anticipates the motor act. •Broca’s aphasia. Speech involves movement selection!

FLLoss of Divergent ThinkingConvergent thinking: just one correct answer e.g. 2+5Divergent thinking: many answers to a question, e.g. function of a pen•FL damage impairs divergent thinking.•Loss of spontaneous speech•Loss of strategy formation (go to get milk)

Frontal subject

FLEnvironmental control: Impaired response inhibition and inflexible behavior•Loss of inhibition. E.g. WCST or Stroop test•Risk taking and rule braking•Self regulation: no autonoetic awareness•Associative learning: can’t associate colors and form or postures (can’t select from set of competing responses the appropriate one)

FLPoor Temporal Memory (Short Term Memory)

Can’t remember Where have you been

Loss of memory to one spot. Monkey can’t

remember theflashing light on theupper right quadrant

Can’t do delayed Nonmatching

to sample

FLImpaired social and sexual behavior•Pseudopsychopathy: show immature behavior, lack of tact and restraint, coarse language, promiscuous sexual behavior, increasedMotor activity lack of social graces. Right Lesion•Pseudodepressed: show apathy, indifference, loss of initiative,reduced sexual interest, little emotion and little or no verbal outputLeft lesion.

Olfaction Deficits

Orbital frontal cortex receives direct projection from the olfactory Bulb. Food doesn’t taste good.

Face symptoms

Spelling deficits, reading problems

FLImaging StudiesRegardless of the nature of the task the the dorsolateral prefrontalcortex is always activated. Why? There is a network of frontalcircuits that is consistentlyrecruited for the solutionof a diverse set of cognitive problems

See Table 16.4

FLDiseases affecting the frontal lobe

•Schizophrenia•Korsakoff•Parkinson•Development (children are bad at FL tests because the frontal lobes

are the last ones to develop)•Aging (old people are bad at FL tests because the frontal lobes are

the first ones to deteriorate)

FL

Neuropsychological Assessment

DISCONNECTION SYNDROMES

A disconnection syndrome is a term introduced by Norman Geschwind to describe the behavioral effects that the interruption of information transferred from one region of the brain to anotherwould have. How? By cutting the cerebral connections

D. M. had problems assembling puzzles because his 2hands could not be coordinated.

Downer’s experiment

When the commissures between the two halves of the brain are disconnected, visual information form one eye can project only to theipsilateral hemisphere.

Anatomy of Cerebral Connections3 major types of neural fibers1. Association Fibers: a)Long bundles (far)

b) U fibers (close)2. Projection Fibers: ascending from the thalamus to the neocortex;

descending form the neocortex to the brainstem and spinal cord.3. Commissural fibers: connect

the two hemispheres. a) Corpus callosum b) anterior commissure c) posterior commissure d) hipocampal commissure

Callosal connections

Anatomy of Cerebral Connections cont…

c) Diffuse: “Random” connections perhaps to awake the otherhemisphere

Commissural connections could be:

a) Topographical: they connect to identical points in the contralateralhemisphere

b) Homotopic: one group of projections goes to areas to which thehomotopic area on the contralateral side projects, e.g

V2L

V1L V2R

Behavioral effects of disconnectionApraxiaAgnosiaAlexiaAgraphiaAcopia

Liepmann’s theory of apraxiaCorpus callosum severed at the genu level

Alexia & Agnosia

Behavioral effects of disconnection cont…

Geschwind model, in which a lesiondisconnects the visual region on theleft from the speech zone or by cccuts. Patient can talk but cannotidentify words or objects because theinformation is disconnected from the speech zone.

Disconnecting sensorimotor systemsOlfaction Vision

Disconnecting sensorimotor systems cont…

Audition: Dichotic-listeningMotor: one hand doesn’t know what the other hand is doingSomesthesis: object placed in a right hand can’t be recognized just by touch.

3 conditions in which the the hemispheres become completely separated:1. Commissurotomy as epilepsy treatment2. Disconnection in animal models (not all animals have a CC)3. Callosal Agenesis: people born without a corpus callosum. The

brain compensates by using the anterior commissure and the brain stem. People show delayed responses in several tasks and in some cases intrahemispheric transfer deficits.

MEMORY

Memory is everywhere

Sources of memory loss1. Infantile amnesia: immature structures?2. Head trauma, drugs3. Transient global amnesia: global ischemia4. Closed head injury5. Electroconvulsive shock therapy6. Amnesia related to diseases: Alzheimer,

Parkinson’s, Korsakoffs

Two general types of amnesia

Can’t formnew

memories

Can’t accessOld

MemoriesPatient H.M.

Kinds of Memory:

1. Explicit Vs Implicit2. Short Vs long termSpecific:Verbal Vs nonverbalVisual Vs auditoryColor Vs formWords vs music

Specific memories imply that there are specific areas andthat memory is everywhere.

Implicit Vs Explicit Memory

Implicit: Unconscious, nonintentional form of memory. E.g. ridinga bicycle, playing football, motor skills.

Explicit: Conscious, intentional recollection of previous experiences.E.g. tell me what did you have for breakfast, what did youdo last Christmas etc.

H.M has no explicit memory (except for very old memories) buthis implicit memory is largely intact

Neural Basis of Implicit Memory

Petri & Mishkin proposed the neocortex and basal ganglia

Case J.K: Parkinson’s patient. Can’t remember how to turn on thelights. Is dopamine important?

Neural Basis of Explicit Memory

Petri and Mishkin proposed that most of the structures responsiblefor explicit memroy are in the temporal lobe

Two Kinds of Explicit MemoryEpisodic Vs Semantic

Episodic: Singular events that a person recalls. Autobiographicalmemory. 3 elements needed: 1) a sense of subjective time2) autonoetic awareness: awareness of yourself as a continuous entity over time, 3) a “self” that can travel in subjectivetime (past, future).

Semantic:Knowledge about the world, all knowledge that is notautobiographical. E.g. historical events, recognition of family, friends, etc.

The Role of the Hippocampus in Memory Scoville and Milner paper: “Loss of recent memory after bilateralhippocampal lesions” H.M. had more than the hippocampus removed.

So what does the hippocampus do?Four theories:1. The hippocampus as a storage site for memory2. The hippocampus and consolidation of new memories3. The hippocampus as a librarian for memories4. Tagging memories with respect to context

Why the confusion about the hippocampus and its role in memory?•Different lesion sizes•Different lesion etiology•Different time of the lesion•Different testing methods

Multiple Memory SystemsNo single region is responsible for all memory. Each region has aSpecific contribution:

Temporal Cortex:RTC lesions: impairments in face-recognition, spatial-position

and maze-learning testLTC lesion: impairments in the recall of word lists, consonant

trigrams and nonspatial associations.

L>R R<L

The Amygdala

Emotional, olfactory and visceral events. It’s contribution is emotionalin nature. E.g. fear conditioning, nice smells-nice events.

The Perirhinal Cortex

The Perirhinal Cortex

Object recognition depends on the rhinal cortex

Rhinal cortex Hippocampus

The diencephalon

Focal lesions of the medial thalamus and patients with Korsakoff’sSyndrome.6 symptoms:1. Anterograde amnesia2. Retrograde amnesia3. Confabulation4. Meager content in conversation5. Lack of insight6. Apathy

Ascending systemsThe basal forebrain

Includes several structures: nucleus basalis, diagonal band, medialSeptum and substantia innominata. These structures are important in the production of acetylcholine, which is then distributed widelythroughout the brain.

Alzheimer’sVanderwolf 5-HT/ACh depletionsDecker ACh/NA depletions

Short Term MemoryAlso called working memory. We use for holding digits, words, names,Or other items in our minds for a brief period. Parallel and separate From long term memory. Temporal lesions produce impairments in short term memorybut not in long term memory.

Lesion to the frontal cortex produce impairments in tasks in which subjects must remember the temporary location of stimuli. Figure shows single cells inArea 8.

Area 8 of the dorsolateral frontal cortex code spatial vision (location of the stimulus) and cells in areas 9 and 46 code for object recognition

Short Term Memory cont…

Summary