Chapter 49 Attention

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Chapter 49Attention

• Presented by Rahnia Parker

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Overview

• What is attention?
• Research correlating attention and sensory
  perception
• Neuronal organization
• Regulating alertness

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ATTENTION

• Because people cant carry out more than one
  cognitive or perceptual task, we need attention
  which can be defined as neural mechanisms that
  enable the selection of stimuli, or tasks, that
  are immediately relevant to behavior.
• Focus on relationship between attention and
  sensory perception (esp. vision)

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Types of attention

• Depends on how, when and what a person attends
  to
• Orientation of eyes, head, and/or body
• Covertly looking at something w/out orienting
• Exogenous stimulus driven from external events
• Endogenous internal goals vs. external
  distractions
• Spatial location of something in space
• Specific objects regardless of location

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STUDIES and what they find

• Spatial cues
• Fig. 49.1
• Symbolic cues most likely target location w/out
  appearing
• Peripheral cues visual stimuli at expected
  target location
• Flashed stimuli as peripheral are powerful attn
  attractors

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Studies cont.

• Neglect Syndrome
• Brain lesions
• Behavior towards contralesional world
• What they see (fig. 49.2)
• Movement in contralesional space
• Not sensory or motor deficits failure to select
  appropriate protions of a sensory representation.

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Studies cont.

• Control of spatial attn
• Studies showing pareital lobe, frontal lobe, and
  anterior cingulate cortex vital
• ERPs (event-related potentials) to measure the
  human spatial attention network
• ERP MRI or PET indirect measures of neural
  activity

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Studies cont.

• Human frontal and pareital cortical areas are
  sources for top-down biasing signals seen in
  visual cortex
• Functional brain imaging studies show the
  following areas are actived in a variety of
  visuospatial tasks requiring spatially directed
  attn
• SPL superior parietal lobule
• FEF frontal eye field
• SEF supplementary eye field
• These areas driven by both attentional feedback
  signals and visual stimulus

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Studies cont

• MONKEY research
• Correlation between selective visual attn and
  neural activity
• Neuron sensitivity selective for stimuli

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Monkey research cont.

• Observations suggesting parietal cortex important
  for shifting attn
• FEF frontal eye field and saccade planning and
  covert attentional selection.
• Organization of spatial attn system might be
  different in monkeys and humans

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Studies cont

• Attention increases sensitivity of vision
• How? Probably increasing neuronal responses
• Pt. C top shows w/out attn lots of overlap btwn
  2 stimuli but bottom shows response with attention

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Studies cont.

• Attention affects neural activity in the human
  visual cortex in the presence and absence of
  visual stimuli
• Event related potential (ERP) and brain imaging
  studies shows selective attn can affect neural
  processing of visual info in human visual cortex
• Attn affects activity of neurons that code an
  attended location and attended stimulus
  attribute.
• Selective attn modulates activity in extrastriate
  areas of visual cortex
• Neural activity affected in presence and absence
  of sensory input

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Studies cont.

• What about in a whole world full of stimuli, how
  does attn select relevant stimuli?
• Wheres Waldo

Efficient and inefficient Bottom line Visual
system is limited
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Studies cont.

• What causes limitations?
• In complex visual situations (wheres Waldo) you
  need to use attention which selects features from
  one location at a time
• Early and late stages of processing may cause
  limitations
• Neurons can only process some signals, not all
• Competition among potentially relevant stimuli
  and biases that determine the outcome of the
  competition
• Attention helps select stimulus in ventral visual
  processing stream and MT and MST of the dorsal
  stream.
• Nonspatial feedback might also bias the visual
  system toward specific target object, not just
  location.

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Studies cont.

• In human visual cortex mechanisms for
  competition btwn multiple stimuli
• Use fMRI to find out
• Certain visual systems activated but stimuli
  presentation suppresses areas (esp. V4 and TEO)

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Studies cont.

• Target selection for eye movement
• Dual task of loci of attention and saccade
• Found that you could
• Give priority to saccade task
• Give priority to perceptual identification task
• Give equal priority to both tasks

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Alertness

• Level of alertness necessary for selective
  attention
• Maintenance from brainstem to cortical and
  subcortical regions of the brain
• ACh
• NE
• DA
• 5-HT

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Alertness cont.

• Monoamines act as neuromodulators
• NE-LC system (LC locus ceruleus in brain stem)
  project neurons to thalamus, cerebral cortex and
  cerebellum
• Three types of task-related activity
• Spontaneous discharge
• Phasic stimulus-evoked responses
• Phasic responses related to physical orienting
  toward given stimulus

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Key Points

• Attention allows us to select tasks that are
  perceived from sensory perception
• Much research is being done to study attention
  and how it works
• The pareital lobe, frontal lobe, and anterior
  cingulate cortex are the areas of the brain
  necessary in attention
• Alertness is regulated by the brain stem and the
  transmitters that it releases

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Chapter 50 - Basic mechanism of learning and
memory

• Associative learning
• Nonassociative learning
• LTP
• LTD

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Associative learning

• Classical conditioning
• Conditioned stimulus (CS)
• Unconditioned stimulus (US)
• Instrumental conditioning
• a process that an organism learns to associate
  with its own behavior

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Nonassociative learning
Siphongill withdrawal reflex
Tailsiphon withdrawal reflex

• Habituation
• Reduction in response
• with repeatedly stimulus
• Dishabituation
• Recovery of habituation after a stronger stimulus
• Sensitization
• An enhanced response after a strong stimulus

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Circuit diagram of two reflexes
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Short term sensitization

• Short-term sensitization PKC-, PKA-, and
  MAPK-induced phosphorylations of different
  substrate proteins

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Long term sensitization

• Long term sensitization active cAMP/PKA pathway
  and induce gene transcription and new protein
  synthesis

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LTP

• LTP a persistent increase in synaptic strength
  (amplitude of EPSP) induced by a brief burst of
  spike activity in presynaptic afferents
• CA3?CA1 synapse best understood pathway
• LTP is related with memory mechanism, but no
  clearly association with any behavioral
  observations

entorhindal cortex
Perforant path
Schaffer collateral path
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LTP cont.

• Classical properties

Weak pathway ?
Strong pathway ?

• Cooperative probability of inducing LTP,
  magnitude of resulting changes, increases with
  of stimulated afferents
• Associativity two distinct axon inputs converge
  into same postsynaptic target
• Input specificity LTP is only induced where
  neuron receives strong input

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Mechanisms of induction of LTP

• Induction of early and late LTP depends on
  intracellular Ca2i
• NMDA receptor-dependent LTP
• - APV and MK-801 block induction of LTP
• NMDAR-independent LTP
• mGluR
• Induction of late LTP
• PKA, MARP

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Mechanisms of LTP expression
? new synaptic contacts

• Six mechanisms

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LTP maintenance/LTD

• Early LTP maintenance needs phosphorylation of
  substrate proteins
• Late LTP maintenance needs gene expression and
  protein synthesis
• Long term depression (LTD) is believed to
  mechanism by which learning is encoded in
  cerebellum
• LTD can be induced by low-frequency stimulation
  over a long period
• LTD share common molecular mechanisms with LTP

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Summary

• Learning associative and nonassociative
• Learning short-term and long-term sensitization
  
• LTP is related with memory
• LTD is related with learning in cerebellum

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Chapter 51

• Learning and Memory
• Brain Systems

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The Highlights

• Case History
• Memory Systems
• Declarative Memory
• Procedural Memory
• Emotional Memory
• The role of the amygdala
• The role of the cerebral cortex

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memory Pronunciation 'mem-rE,

• 1 a the power or process of reproducing or
  recalling what has been learned and retained
  especially through associative mechanisms b the
  store of things learned and retained from an
  organism's activity or experience as evidenced by
  modification of structure or behavior or by
  recall and recognition2 a commemorative
  remembrance b the fact or condition of being
  remembered 3 a a particular act of recall or
  recollection b an image or impression of one
  that is remembered c the time within which past
  events can be or are remembered
• 4 a a device or a component of a device in
  which information especially for a computer can
  be inserted and stored and from which it may be
  extracted when wanted b capacity for storing
  information
• 5 a capacity for showing effects as the result
  of past treatment or for returning to a former
  condition -- used especially of a material (as
  metal or plastic)

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Case History

• Age 9 sustained laceration to supraorbital
  region
• Tests consistently failed to show any localized
  epileptogenic area
• Bilateral medial temporal lobe resection
  performed
• So what? Central to later ideas about multiple
  memory systems

Fig. 51.1
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Memory Systems

• defined by both a unique set of operating
  characteristics and by unique brain structures
  and connections.
• The anatomical pathways of the different memory
  systems are not entirely separate.

Fig. 51.2
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Declarative Memory

• Major components cerebral cortical areas,
  cortical areas surrounding hippocampus, and
  hippocampus

Figure 51.3
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A Few Studies


Figure 51.6
(B) Outline of odor pairings used in training on
two sequential sets of paired associates, plus
stimuli used in tests for transitivity (C for A
Z for X) and symmetry (B for C Y for Z).
Figure 51.5
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Procedural Memory

• habits, skills and sensori-motor adaptations
  that occur constantly in the background of all of
  our intentional and planned behavior.
• 2 subsystems
• 1.Neostriatal
• 2.Cerebellar

Place vs. response learning
Figure 51.9
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Emotional Memory

• Mediate preferences and aversion
• Amygdala plays critical role in fear conditioning

Figure 51.12
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A Few More Studies


Emotional Memory

Procedural Memory
Figure 51.10
Figure 51.13
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Amygdala and Memory

• Emotional events activate SNS and HPA axis

Figure 51.14
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Cerebral Cortex and Memory

• Provides detailed information to the
  aforementioned memory systems
• Experience-driven plasticity in adult cerebral
  cortex
• Removal of sensory input to primary sensory areas
  causes a reorganization
• Semantic memory
• Priming
• Working Memory

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What to remember

• Amygdala has outputs to both of the other memory
  systems (declarative and procedural)
• Cerebral cortex contributes substantially to all
  three systems
• There is some overlapping among the three memory
  systems
• Learning and memory can be highly variable among
  individuals

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Questions?