THE FRONTAL LOBE

v FL Function: It is the end point for the visuomotor and object- recognition functions. The frontal lobe selects behaviors with respect to context and internalized knowledge. Separated from the parietal lobe by the central fissure and from the Temporal lobe by the Sylvian Fissure.Constitutes 20% of all the 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) also called orbital frontal c) Medial frontal (25, 32)

FL Connections 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 superior colliculus to control eye movement.

FL Connections cont… The prefrontal areas are the end points of the dorsal and ventral streams 1.Dorsolateral prefrontal (9, 46) receives inputs from the PP areas and the STS (reciprocal connections). Connections to cingulate cortex, basal ganglia and superior colliculus. DA projections form the basal ganglia And the ventral tegmentum

FL Connections 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.

FL Theory 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 Cortex The 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)

FL Theory of F.L Function cont… Prefrontal Cortex Controls cognitive processes necessary to make the movements at correct time and place. Could be controlled by internal or external or it 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 a behavior. E.g. shoe store on your way to buy milk. C)Context: Multiple simultaneous roles, rules of behavior. E.g. how to act with your friends vs. your grandma D)Autonoetic Awareness: awareness of yourself as a continuous entity over time. Autobiographical memory

FL Frontal Lobe Symptoms 1.Motor disturbance 2.Loss of divergent thinking 3.Environmental control 4.Poor temporal memory 5.Impaired social & sexual behavior 6.Olfaction deficits 7.Face symptoms

FL Motor 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!

FL Loss of Divergent Thinking Convergent thinking: just one correct answer e.g. 2+5 Divergent 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

FL Environmental 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)

FL Poor Temporal Memory (Short Term Memory) Can’t remember Where have you been Loss of memory to one spot. Monkey can’t remember the flashing light on the upper right quadrant Can’t do delayed Nonmatching to sample

FL Impaired social and sexual behavior Pseudopsychopathy: show immature behavior, lack of tact and restraint, coarse language, promiscuous sexual behavior, increased Motor activity lack of social graces. Right Lesion Pseudodepressed: show apathy, indifference, loss of initiative, reduced sexual interest, little emotion and little or no verbal output Left lesion. Olfaction Deficits Orbital frontal cortex receives direct projection from the olfactory Bulb. Food doesn’t taste good. Face symptoms Spelling deficits, reading problems

FL Imaging Studies Regardless of the nature of the task the the dorsolateral prefrontal cortex is always activated. Why? There is a network of frontal circuits that is consistently recruited for the solution of a diverse set of cognitive problems See Table 16.4

FL Diseases 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 another would have. How? By cutting the cerebral connections D. M. had problems assembling puzzles because his 2 hands 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 the ipsilateral hemisphere.

Anatomy of Cerebral Connections 3 major types of neural fibers 1.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 other hemisphere Commissural connections could be: a)Topographical: they connect to identical points in the contralateral hemisphere b)Homotopic: one group of projections goes to areas to which the homotopic area on the contralateral side projects, e.g V2 L V1 L V2 R

Behavioral effects of disconnection Apraxia Agnosia Alexia Agraphia Acopia Liepmann’s theory of apraxia Corpus callosum severed at the genu level

Alexia & Agnosia Behavioral effects of disconnection cont… Geschwind model, in which a lesion disconnects the visual region on the left from the speech zone or by cc cuts. Patient can talk but cannot identify words or objects because the information is disconnected from the speech zone.

Disconnecting sensorimotor systems OlfactionVision

Disconnecting sensorimotor systems cont… Audition: Dichotic-listening Motor: one hand doesn’t know what the other hand is doing Somesthesis: 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 treatment 2.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 loss 1.Infantile amnesia: immature structures? 2.Head trauma, drugs 3.Transient global amnesia: global ischemia 4.Closed head injury 5.Electroconvulsive shock therapy 6.Amnesia related to diseases: Alzheimer, Parkinson’s, Korsakoffs

Two general types of amnesia Can’t form new memories Can’t access Old Memories Patient H.M. Kinds of Memory: 1.Explicit Vs Implicit 2.Short Vs long term Specific: Verbal Vs nonverbal Visual Vs auditory Color Vs form Words vs music Specific memories imply that there are specific areas and that memory is everywhere.

Implicit Vs Explicit Memory Implicit: Unconscious, nonintentional form of memory. E.g. riding a bicycle, playing football, motor skills. Explicit: Conscious, intentional recollection of previous experiences. E.g. tell me what did you have for breakfast, what did you do last Christmas etc. H.M has no explicit memory (except for very old memories) but his 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 the lights. Is dopamine important?

Neural Basis of Explicit Memory Petri and Mishkin proposed that most of the structures responsible for explicit memroy are in the temporal lobe

Two Kinds of Explicit Memory Episodic Vs Semantic Episodic: Singular events that a person recalls. Autobiographical memory. 3 elements needed: 1) a sense of subjective time 2) autonoetic awareness: awareness of yourself as a continuous entity over time, 3) a “self” that can travel in subjective time (past, future). Semantic:Knowledge about the world, all knowledge that is not autobiographical. 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 bilateral hippocampal 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 memory 2.The hippocampus and consolidation of new memories 3.The hippocampus as a librarian for memories 4.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 Systems No single region is responsible for all memory. Each region has a Specific contribution: Temporal Cortex: RTC lesions: impairments in face-recognition, spatial-position and maze-learning test LTC 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 emotional in nature. E.g. fear conditioning, nice smells-nice events. The Perirhinal Cortex

Object recognition depends on the rhinal cortex Rhinal cortexHippocampus

The diencephalon Focal lesions of the medial thalamus and patients with Korsakoff’s Syndrome. 6 symptoms: 1.Anterograde amnesia 2.Retrograde amnesia 3.Confabulation 4.Meager content in conversation 5.Lack of insight 6.Apathy

Ascending systems The basal forebrain Includes several structures: nucleus basalis, diagonal band, medial Septum and substantia innominata. These structures are important in the production of acetylcholine, which is then distributed widely throughout the brain. Alzheimer’s Vanderwolf 5-HT/ACh depletions Decker ACh/NA depletions

Short Term Memory Also 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 memory but 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 in Area 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