Cognitive Neuroscience Cortical Hemispheres Attention Language

Transcription

1 Cognitive Neuroscience Cortical Hemispheres Attention Language Based on: Chapter 18 and 19, Breedlove, Watson, Rosenzweig, 6e/7e.

2 Cerebral Cortex Brain s most complex area with billions of neurons and trillions of synapses: the tissue responsible for mental activities Consciousness Perceives sensations Commands skilled movements Emotional awareness Memory, thinking, language ability Motivation All higher mental functions

3 Cerebral Cortex Types of Cerebral Cortex Neocortex Newest in evolution About 90% of total cortex in humans 6 layers, most complex

4 Cerebral Cortex Types of Cerebral Cortex, cont d Most of the human brain cortex is association cortex. Functions of the association cortex have been more difficult to discover than those of any other brain areas. Association cortex is unimodal (modality specific) or heteromodal (higher order).

5 Language is lateralized in humans. The left hemisphere is dominant for language in over 95% of righthanders and 60-70% of left-handers. Many left-handers have significant bilateral language function. After a left hemisphere injury left handers tend to recover language more quickly than righthanders. Cerebral Cortex Lateralization in the Cerebral Cortex

6 Wada and Ramussen (1960) Cerebral Cortex Lateralization in the Cerebral Cortex Injection of Na-amytal (amobarbital, brief anesth.) into a. carotis int. on one side Segregation of functions btw. the two hemishpheres fusiform gyrus - A region on the inferior surface of the cortex, at the junction of temporal and occipital lobes, that has been associated with recognition of faces.

7 Cerebral Cortex Lateralization in the Cerebral Cortex Split-Brain Studies Sperry (1950s) Split-brain procedure Cutting axons making up the corpus callosum to treat convulsions (callosotomy, comissurotomy) No major deficits However, with proper experiments, subjects behaved as if they had 2 brains

8 Cerebral Cortex Split-brain studies, cont d Left Hemisphere Language Dominance Right visual field, repeated easily Left visual field, difficulty verbalizing Image only in left visual field, object in left hand, unable to describe Split-brain Unable to describe anything to left of visual fixation point

9 Split brain (cont d) Cerebral Cortex

10 Cerebral Cortex Dichotic auditory presentation and the right ear advantage Broadbent (1953) theory of selective attention (response is grouped by hemispheres) Kimura (1973) - the dominant hemisphere responds more precisely - only the dominant hemishphere responds to simultaneous stimuli

11 Cerebral Cortex Structural asymmetry of the human planum temporale

12 Cerebral Cortex General comparison of functions dedicated to each hemispheres Left vs. right Linear vs. holistic Logic vs. intuitive Sequential vs. random Symbolic vs. concrete Verbal vs. non-verbal Reality based vs. fantasyoriented Source:

13 Attention Attention Selects Stimuli for Processing There are limits on attention Attention filters information early or late in sensory processing

14 Attention Attention may be endogenous or exogenous With endogenous attention, we choose which stimuli to focus on In exogenous attention, stimuli grab our interest We use visual search to make sense of a cluttered world Eriksen: Flanker task; Eriksen-Posner: Attention Network Task (ANT)

15 Attention We use visual search to make sense of a cluttered world

16 Attention

17 Attention Reaction-Time Responses, from Input to Output Electrophysiological Techniques Trace Rapid Changes of Brain Activity Voluntary shifts of attention produce unique patterns of electrical activity Reflexive visual attention has distinctive electrophysiological effects P1 and N1

18 Attention Many Brain Regions Are Involved in Processes of Attention Neuroimaging confirms that the anatomical foci of attention show augmented processing (example of the visual cortex below)

19 Attention Many Brain Regions Are Involved in Processes of Attention Attention alters the functioning of individual neurons The superior colliculus guides attentional eye movements The pulvinar drives shifts of attention Several cortical areas are crucial for generating and directing attention

20 Attention Many Brain Regions Are Involved in Processes of Attention The superior colliculus guides attentional eye movements The pulvinar drives shifts of attention

21 Attention Two Cortical Networks Collaborate to Govern Attention A dorsal frontoparietal system provides top-down control of endogenous attention A right temporoparietal system facilitates bottom-up control of exogenous attention

22 Attention Disorders Provide Clues about the Organization of Attention Neglect of one side of the body and space can result from parietal lobe injury In Bálint s syndrome, narrowed attention combines with spatial disorientation

23 Attention Disorders Provide Clues about the Organization of Attention Neglect of one side of the body and space can result from parietal lobe injury In Bálint s syndrome, narrowed attention combines with spatial disorientation Subcortical mechanisms are compromised in progressive supranuclear palsy Difficulty with sustained attention can sometimes be relieved with stimulants

24 Attention The Frontal Lobes Govern Our Most Complex Behavior Frontal lobe injury in humans leads to emotional, motor, and cognitive changes Neuroeconomics identifies brain regions active during decision making

25 Attention and Consciousness

26 Language A system by which sounds, symbols, and gestures used for communication Language processing: Language comes into brain through visual and auditory systems Motor system: Produces speech, writing Processing between sensory and motor systems Phonemes, morphemes, semantics, syntax, grammar Sensitive period Language has both learned and innate components Many nonhuman species engage in elaborate vocal behavior

27 Aphasia Language Discovery of specialized language areas in the brain Partial/complete loss of language abilities following brain damage Greek/Roman Empires: Tongue control speech Sixteenth century: Speech impairment, tongue not affected 1770: Gesner, brain damage 1825: Bouillard, frontal lobes 1861: cortical area in frontal lobe

28 Language Discovery of specialized language areas in the brain, cont d Broca s area (BA 44-45) Paul Broca in 1864: Region of dominant left frontal lobe, articulate speech Wernicke s area (BA 42,22) Karl Wernicke in 1874: Superior surface of temporal lobe between auditory cortex and angular gyrus, lesions disrupt normal speech

29 Language Specialized language areas in the brain Types of Aphasia Broca s Aphasia (motor, nonfluent aphasia) Difficulty speaking, but understand spoken/heard language Paraphasic errors Pause to search for words, repeat overlearned things, difficulty repeating words Wernicke s aphasia (sensory, fluent aphasia) Speech fluent, comprehension poor Correct sounds, incorrect sequence Comprehension difficult to assess Playing music, writing similar Storing memories of sounds that make up words Characteristics: Correct words in incorrect sequence, incorrect word similar to correct word

30 Aphasia and the Wernicke- Geschwind Model Broca s area Wernicke s area Arcuate Fasciculus Angular gyrus Problems with model Language

31 Aphasia and the Wernicke-Geschwind Model

32 Language Conduction Aphasia Lesion of fibers composing arcuate fasciculus Comparison with Broca s aphasia, Wernicke s aphasia: Comprehension good, speech fluent Difficulty repeating words Symptoms: Repetition substitutes/omits words, paraphasic errors, cannot repeat function, nonsense words, polysyllabic words

33 Language Aphasia Summary Table

34 Language Language Studies Using Brain Stimulation and Brain Imaging Language Studies Old methods: Correlate language deficits with postmortem analysis of brain damage Recent techniques Study language function in brains of living humans: Electrical brain stimulation and PET The Effects of Brain Stimulation on Language Three main effects: Vocalizations, speech arrest, speech difficulties similar to aphasia

35 Language Language Studies Using Brain Stimulation and Brain Imaging The Effects of Brain Stimulation on Language (Cont d) Motor cortex: Immediate speech arrest Broca s area: Speech stopped after strong stimulation, speech hesitation from weak stimulation Posterior parietal lobe near Sylvian fissure and temporal lobe: Word confusion and speech arrest George Ojemann: Small parts of cortex: naming, reading, repeating facial movements

36 Language Language Areas Shown by Neuroimaging (Posner és Raichle, 1994)

37 Functional Neuroimaging of Language Forrás: Posner and Raichle, 1994

38 Language Partial Recovery from Damage to Language Areas

39 Language Summary of Language processing Initial activity in visual cortex, then activity in motor cortex corresponding to muscles that move vocal apparatus Multiple brain areas critical for language Language skills: Naming, articulation, grammar usage, comprehension Further brain imaging studies will reveal more about language systems organization

40 . for attention!