8_Cortical - Chapter 8: Cortical behavior Behavior in the...

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Unformatted text preview: Chapter 8: Cortical behavior Behavior in the brain Cortical areas according to brain lobe Left and right brain Some cortical functions / syndromes Language Gnosia Attention Praxia Executive functions Memory Summary Behavior in the brain Behavior Sensory processing (sensation) (perception) 1 Reception in the cortex: sensation (primary sensory area) After reception: perception (association areas) Sensory processing Association areas and sensation (perception) 1. Object 2. Image: from eye to brain => sensation (detection, gewaarwording) 3. Processing in the brain => perception (waarneming) ! Perception is possible without sensation a subliminal stimulus passes below the normal limits of sensation FUNCTIONAL organization of the human cerebral cortex into 4 areas: 1. idiotypic cortex: 2. unimodal or modality specific association cortex: primary C. secondary C. higher order C. 3. heteromodal or multimodal association cortex: cognition 3. limbic and paralimbic cortex: emotion Hierarchical organization: - sensation (detecting) - perception (process of integrating, recognizing, interpreting) Functional segregation: each level contains functionally distinct areas Parallel processing: simultaneous analysis of a signal in different ways (eg an unconscious and a conscious stream, dorsal and ventral stream) 2 Unimodal association areas (secondary areas, higher order) Primary areas have direct afferent (sensory) or efferent (motor) connections with sensorory or motor systems. In rat, these areas occupy nearly all the cortex, in human only 20% Multimodal association areas Anatomy and physiology, 4 Action starts from prim. motor c. structure and function meet. Multimodal association areas modulate information between secondary areas 3 Fiber tracts (forming the white matter) connect different regions How do these different cortices work together? - Short loop pocesses do not need the cortex, eg tendon reflexes. - Medium loop pocesses mediate rapid, but simple, responses (e.g.swapping a mosquito). - Long loop pocesses (e.g.writing down the name of a seen object), require the complex processing power of the association areas. Unimodal Multimodal U-fibres connect adjacent zones (Crevits, Mijn geest van vlees en bloed, 2007) 4 • Frontal lobes – Three distinct areas: • M1 primary motor cortex Cortical areas according to brain lobe with emphasis on “higher” functions • PM premotor region (motor association cortex) • PF prefrontal region (multimodal asso cortex) PFC (prefrontal cortex) Damage may lead to an array of difficulties e.g. intact IQ and academic skills, but failure to organize a sequence of behaviors to attain a goal From a responsible, religious, respectable and socially well-adapted man to an irreverent, profane and impulsive itinerant. Relatively immature in children e.g. perseveration in young children; repeated behavior 1848, a milestone in neurosciences: key parts of personality reside in the frontal lobe. These findings indirectly lead to the development of lobotomy to help some people with severe mental derangement. 5 Phineas Gage’s skull (The Warren Museum) The bar that was shot through the head of Mr. Phineas P. Gage at Cavendish, Vermont, Sept. 14, 1848. (Museum of the Medical College of Harvard University) The frontal lobe contains the prefrontal multimodal association area for motor and sensory control (executive functions, working memory) Frontal lobotomie (Nobelprice to Moniz in 1949) Major areas of the prefrontal cortex Anterior cingulate 6 Prefrontal syndromes (classical view) Prefrontal syndromes (changing view) 1. Dorso-lateral-prefrontal cortex (DLPFC) Executive functions, working memory dopamine lesion: executive and memory dysfunctions Classical view: Executive functions (problem solving, abstracting, planning, strategy development and implementation) and working memory: DLPFC 2. Orbito-frontal cortex Integration of (limbic) emotional and behavioral responses serotonin lesion: dysfunctions of mood and personality disorders 3. Anterior cingulate cortex Motivational behaviour noradrenaline lesion: obsessive-compulsive disorders Newer view: -Metacognitive executive functions: cognitive control problem solving, abstracting, planning, strategy development and implementation, and working memory: ~ dorso-lateral-prefrontal cortex -Emotional / motivational executive functions: coordination of cognition and emotion the ability to fulfill basic impulses following socially acceptable strategies ~ orbito-frontal and medial frontal cortex (Ardila A., Brain and Cognition 2008, 68, 92–99) The parietal lobe makes part of the parieto-temporo-occipital multimodal association area Parietal cortex S1 primary somatosensory cortex SA somatosensory association cortex MMA multimodal association cortex (attention, language, praxia, spatial orientation) 7 • Parietal association area • Parietal association area – effect of damage – Integration of information from various sensory modalities – Integration of information from senses and information from memory – Integration between individual’s internal state and the external (sensory) world e.g. “where” an object is, requires integration of various information (where route) Attentional defects in right parietal lobe lesion – ALEXIA (inability to read) AGRAPHIA (inability to write) – APRAXIA (failure to generate purposeful movements) e.g. can not stir milk in coffee, but can pantomime the action – Loss of spatial processing and attentional deficits. Temporal cortex Lateral Primary auditory cortex (BA 41) Auditory association cortex (BA 42) Wernicke area (BA 22) THE LATERAL TEMPORAL LOBE IS CRITICAL FOR LANGUAGE AND MUSIC COMPREHENSION Left hemispatial neglect The lack of attention to one side of space, usually the left, as a result of (right) parietal lobe damage, despite intact sensory and motor functioning. The neglect is relative to the midline of the body. In severe cases, the patient denies the left side of his own body (hemisomatagnosia) Medial (limbic system) MOVE AM amygdala HC hippocampus FX fornix SPT septum MB mammillary bodies OB olfactory bulb THE MEDIAL TEMPORAL LOBE IS CRITICAL FOR EMOTION AND MEMORY 8 Temporal cortex The lateral temporal lobe makes part of the multimodal parieto-temporooccipital multimodal association area => see language, memory, limbic system, emotion THE LATERAL TEMPORAL LOBE IS CRITICAL FOR LANGUAGE AND MUSIC COMPREHENSION Auditory Wernicke Semantic memory THE MEDIAL TEMPORAL LOBE IS CRITICAL FOR EMOTION AND MEMORY MOVE Occipital cortex Visual information => primary visual cortex (V1): retinotopic organization Occipital cortex: naming in human and macaque Human segregation of visual information: form, color, motion, depth, etc. in visual association cortices Macaques 9 Occipital cortex: ‘What and Where’ pathways (MT) Higher visual pathways: SIMPLIFIED versus more REALISTIC Dominance in the brain Left and right brain Dominance is defined by language 10 Lateralisation exists in different vertebrates e.g. chicken (!!! in chickens, the visual pathway is entirely crossed) left eye left occipital Laterality right eye right occipital cortex In the same time, chickens use their -right eye (left occipital) to discriminate grains from littele stones (detail) -left eye (right occipital) to notice predators (the Gestalt) Advantage: two functions simultaneously Disadvantage: when one cortex has been destroyed, that function has lost. And in humans? Dominance is defined by language 96 % of righthanded people have their dominant hemisphere on the left 70 % of lefthanded people have their dominant hemisphere on the left (Rasmussen, 1991) 11 Laterality and the influence of culture: holistic versus analytic perception Dominant hemisphere lesion: aphasia Arcuate fascicle Westerners tend to engage in context-independent and analytic perceptual processes Asians tend to engage in context-dependent and holistic perceptual processes Nisbett et al., Trends in Cognitive Sciences 2005, 9, 467-73 Nondominant hemisphere lesion • Inattention (neglect for left side) • Denial or unconcern • Extinction (on double simultaneous sensory stimulation) • Delirium • Constructional apraxia • Dressing apraxia • Amusia • Spatial disorientation 12 What do you see? The large H or the S? Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht teh frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Gestalt The right hemisphere is specialized in face recognition Hearing in the brain PS It would be wrong to think that only the limbic system is involved in emotion. The neocortex also plays part. We sometimes have strong emotional reactions only after consciously thinking (by the neocortex). ? Vissarion Shebolin (1902-1963, conservatory of Moskou) continued to compose after a left hemisphere stroke causing aphasia 13 Hearing in the brain Left hemisphere: rythm Right hemisphere: melody (analytic) (holistic) Major cortical functions / syndromes The Sapir-Whorf hypothesis (the “linguistic relativity hypothesis")* postulates a systematic relationship between the grammatical categories of the language a person speaks and how that person both understands the world and behaves in it. Language Hopi-indians in Arizona have no word for present, past and future. They have another notion of time. This idea challenges the possibility of perfectly representing the world with language, because it implies that the mechanisms of any language condition the thoughts of its speaker community. *According to the antropologist Edward Sapir and his student Benjamin Whorf 14 The Sapir-Whorf hypothesis (the “linguistic relativity hypothesis") The Sapir-Whorf hypothesis (the “linguistic relativity hypothesis") Can we think without language? Can we think without language? not as detailed, but - deaf-mute persons do think - aphasia patients have normal non-verbal intelligence (Crevits L., 2007, Mijn geest van vlees en bloed) Communicative gesture in a baboon. An adult female intimidates another individual by quickly rubbing her right hand on the ground. Language may have evolved from a gestural system "mirror neurons" might have given chimpanzees the mental power to recognize subtle differences in hand gestures however, in 2005, the first experiment showing that vocal sound of chimps can carry meaning for chimpanzees (Slocombe and Zuberbuhler, Oct. 2005, Current Biology) => perhaps language got its start with rough grunts, rather than hand waving Report of the first evidence of strong population-level right-handedness in 60 captive baboons for a species-specific communicative manual gesture supports the view that lateralization for language may have evolved from a gestural system of communication controlled by the left hemisphere. Behavioural Brain Research 171 (2006) 170–174 15 Intermezzo: mirror neurons Mirror neurons fire both when an animal acts and when the animal observes the same action performed by another. Theory of Mind (mind reading) involves the amygdala, sup. temp. region, medial frontal and orbitofrontal cortex Thus, the neuron "mirrors" the behavior of another animal, as though the observer were itself acting. They have been observed in primates, in humans and in some birds. In humans, brain activity consistent with mirror neurons has been found in the premotor cortex and the inferior parietal cortex The function of the mirror system is a subject of further research. Mirror neurons may be important for understanding the actions of other people, and for learning new skills by imitation. Some researchers argue that mirror systems contribute to the theory of mind. Others relate mirror neurons to language abilities. It has been proposed that problems with the mirror system may underlie some disorders, especially autism. Typically impaired in autism … back to language Language from gestures or from grunts? Anyway, … Even if language got started with grunts (verbally), mirror neurons may still have played an important part in the evolution of communication. Interpreted in Language and speech - Some of the regions where monkeys have mirror neurons correspond to areas of the human brain that handle language. - What is more; mirror neurons are also linked to the ability to get inside other people's heads and understand their intentions. It is one thing to figure out why someone else is making a rough grunt. Auditory cortex And … when you know that other people are trying to figure out what your rough grunt means, you have got a conversation. 16 Aphasia: major historical landmarks Language disorders • Aphasia: acquired disorder of language • Associated disorders: – Alexia – Agraphia Note: Dysarthria: disorder of the motor apparatus of speech Wernicke • Broca (1861): patient with loss of speech, but good comprehension • Wernicke (1874): fluent speech, but poor comprehension • Lichtheim (1885): classic description of aphasic syndromes Broca: production of language: motor drive + grammar motor (expressive, Broca) aphasia: “…” “… I house…walk … house” Wernicke: comprehension sensory (receptive, Wernicke) aphasia: “and when he walked, and the store closed, it was” PS Even in language, both hemispheres work together Left hemisphere: phasia Right hemisphere: - spoken language: aspects of affection, prosodia, singing - written language: if damaged => omission, wrong spliting, difficult to write on a straight line, repeating of letters 17 Repeat spoken words Repeat written words From spoken or written words to speech Fundamental lessons from aphasia • Language processors are localized • Language is distributed in the brain • Language processors are regionally associated with different parts of the brain in proximity to sensory or motor functions Premotor cortex • Different language problems can be due to an underlying deficit in a single language processor Visual cortex Finally, the motor cortex drives to move mouth, tongue … => speech 18 GNOSIA (recognition) Agnosia •A recognition (perception) problem (normal sensation) •The inability to recognize objects when using a given sense and when that sense is basically intact •Modality specific: visual, auditive, tactile How do we know that dogs are dogs and not cats? Visual agnosia Agnosia in non-visual modalities Auditory agnosia (sup. temp. lesions, usually bilateral) Word deafness Auditory sound agnosia Amusia Tactile agnosia (inf. parietal / insula lesions) Can not recognize objects by touch somatosensory association cortex Visual agnosia: disorder of the vental stream 19 Hemispatial visual neglect Attentional defects PRAXIA: the generation of purposeful movements APRAXIA: failure to generate purposeful movements despite normal motor function lesion mostly in left parietal cortex Ideational A.: inability to describe can pantomime Ideomotor A.: can describe can not pantomime These patients with right parietal damage typically orient eyes and head towards the right side. They were not looking to a certain target situated on the right side. (The room was empty with only the photographer standing right in front of them.) 20 Ideational Apraxia Ideomotor Apraxia • Inability to correctly formulate the ideational concepts for carrying out a multistep activity in either site of the body • Can pantomime • Inability to correctly perform learned skilled movements, when this deficit cannot be attributed to weakness, sensory loss, etc. • Great difficulty in attempting to pantomime an action (e.g., sawing a piece of wood, using a phone); improves with repetition, and best when using actual object • Lesion: left parietal-temporal-occipital region • Lesion: left inferior parietal lobe or SMA Executive functions (DLPFC) Classifications of apraxia 1. According to disturbed function: - ideomotor A: left parietal - ideational A: left parietal-temporal-occipital 2. According to location: e.g.oral (bucco-facial) A: left anterior 3. According to prominent symptom: e.g. constructive A: multiple locations LHD03 M ODE L RHD01 LHD08 M ODE L RHD06 LHD01 M ODE L RHD10 The ability to think abstractly and to plan, initiate, sequence, monitor, and stop complex behaviour. LHD10 Executive dysfunction associated with apathy, attention deficit (ADHD), negative symptoms in schizophrenia, treatment response in depression... M ODE L RHD05 Different projections from the subcortex to the DLPFC. 21 Executive functions and attention Executive functions and solving of conflicts Selective attention (concentration on one source of information) can be conceptualized: - as an executive process an sich – or, - as an essential component of different executive processes ACC: recognition and correction of the conflict DLPFC: monitoring of goals and allocation of selective attention ⇒ executive functions are closely related to working memory and attention ⇒ remember: central executive in the working memory model of Baddeley supervisory attentional system (SAS) in the Norman &Shallice model ACC: intermediate function in emotional control subjective experience of pain. ACC DLPFC Memory Processes: R-R-R-(R) Registration - Retention - Retrieval (Reproduction) Rehearsal Sight Memory Elaboration and Organization Smell Sound Sensory Memory Attention Short-Term Memory Long-Term Memory Retrieval Taste Touch Lost Lost Control processes: attention, rehearsal, coding, retrieval 22 During the process of LTM, two kinds of changes occur: 1. 2. Working Memory Development of new synapses (synaptogenesis), esp in childhood Modulation of synaptic connections giving rise to networks with permanent structural changes => engram through long term potentiation and long term depression LTP is a mechanism by which short-term memories move into long-term storage. Declarative memory refers to all memories that are consciously available. These are encoded by the hippocampus, but consolidated and stored in the neocortex. Declarative memory has two major subdivisions: • Episodic memory refers to memory for specific events in time. • Semantic memory refers to knowledge about the external world, e.g.the function of a pencil, the name of the president. Procedural memory refers to the use of objects or movements of the body, such as how exactly to use a pencil or ride a bicycle. This type of memory is encoded and stored by the basal ganglia, cerebellum and supplementary motor cortex. Two glutamate receptors: AMPA: alfa-amino-3-hydroxy-5methyl-4-isoxazole-propionic acid NMDA: N-methyl-D-aspartate Long-term potentiation (LTP) Hippocampus CA1 The CA1 region of the hippocampus is essential for long-term memory. Over time, these synapses become increasingly sensitive => a constant level of presynaptic stimulation becomes converted into a larger postsynaptic output: LTP. Mg-ions block the canal glutamate no influx LTP in rat brains coincides with the formation of additional synapses between the presynaptic axon terminal and the dendrite it synapses with. LTP has also been demonstrated in neurons of the cerebellum. influx of Na+ Toni, N., et al, Nature, 25 Nov 1999 enhanced influx of Na+ influx of Na+ and Ca2+ The AMPA-receptors let enter Na+, after binding to glutamate. Mg-ions block the canal of the NMDA-receptor and prevent the influx of ions. When the cell is partially depolarised, Mg-ions move away. Na+ and Ca2+ can enter the cell. 23 Long-Term Depression (LTD) Ca2+ ions flow into the cell through the NMDA receptors and bind to calmodulin. This activates calcium-calmodulin-dependent kinase II (CaMKII). CaMKII phosphorylates AMPA receptors making them more permeable to the inflow of Na+ ions and thus increasing the sensitivity of the cell to depolarization. Slow, weak stimulation of CA1 neurons brings about long-term changes in the synapses. In case of LTD, a reduction in the sensitivity occurs: Glu binds to a different type of NMDA receptor. CaMKII may also increase the number of AMPA receptors at the synapse. Increased gene expression (i.e. protein synthesis, perhaps of AMPA receptors) also occurs during the development of LTP. Additional synapses may also form during the formation of LTP. Long-term depression occurs in the cerebellum of mice during the development of a conditioned response. Memory Processes: anatomy • Ultra short term memory (sensory) • Short term memory (working): prefrontal cortex ability to recall things within 10 sec. and to do something with that info – Must be rehearsed to keep it there longer – Lost if not transferred to long term memory Four selected memory systems DLPFC • Long term memory: information retained Declarative memory (explicit): - Episodic: medial temporal (hippocampus) - Semantic: lateral temporal Procedural memory (implicit): Basal ganglia, cerebellum and supplementary motor cortex Episodic memory (medial temporal lobe) 24 Interaction of different brain regions in encoding and retrieval Episodic memory (medial temporal lobe): circuit of Papez, the hippocampo-mammillo-thalamic axis (hippocampus-fornix-mammilary body-thalamus-cingulate-neocortex) Retrograde and anterograde amnesia Retrospective and prospective memory Retrospective memory: see abobe Prospective memory: remembering to remember or remembering to perform an intended action. Retrograde amnesia: a form of amnesia where someone will be unable to recall events that occurred before the onset of amnesia. Anterograde amnesia: a loss of memory of what happens after the event that caused the amnesia. Instead of recalling past actions events, or knowledge (retrospective memory), prospective memory is self-initiated and does not operate directly on external stimuli. e.g. remembering to take certain documents to the office, remembering to call someone at night, remembering to take a medicine in the evening. 25 Suppression of memory After all… It is clear that remembering is not exactly reproducing. Memory is a dynamic process that (easily) can be influenced e.g. by emotions. Not only the sensation, and the perception are distortions of reality, memory also is a modulated reproduction. While subjects try to suppress memories, the prefrontal cortex becomes more active and the hippocampus less active. Crevits L., Mijn geest van vlees en bloed, 2007 False memories Our memories are coloured and distorted! cf experiment FUNCTIONAL organization of the human cerebral cortex into 4 areas: 1. idiotypic cortex: What was the speed of these cars when they crashed 95 they touched each other 40 The brain is very flexible, ever making new connections (experience). People with frontal damage are very susceptible to false memories, even to inventions because their frontal control mechanism (the monitor) has been lesioned. 2. unimodal or modality specific associationcortex: primary C. secondary higher order 3. heteromodal or multimodal associationcortex: cognition 3. limbic and paralimbic cortex: emotion 26 Left and right brain work togheter Structures connecting both hemispheres: corpus callosum commissura anterior commissura posterior The cortex needs … the corpus callosum c. callosum comm. commissura anterior posterior The cortex needs … the corpus callosum Pioneer: Sperry (Nobelprice 1981) Humans: Experiments with tachistoscope (~ section of chiasma opticum) Experiments with rats: section of corpus callosum & optic chiasm Seen from the standpoint of the testperson 27 The cortex needs … the corpus callosum Seen from the standpoint of the testperson Humans: Experiments with tachistoscope (~ section of chiasma opticum) in split-brain patients (~ section of corpus callosum) Chimera composed of 2 half faces, exposed for 0.15 s in a tachistoscope. With spoken response (LH), the patient retrieves the right face. With pointing (non-verbal, RH), the patient chooses the left face. Cognitive functions contributing to mental performance are distinct but heavily intermingled. 28 ...
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This note was uploaded on 05/28/2010 for the course GE BIOL020000 taught by Professor Luccrevits during the Spring '10 term at Ghent University.

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