Attention and Working Memory Notes

Attention and Alertness

  • Alertness: Current level of sensitivity or responsiveness to environmental cues.
  • Attention: Actively processing specific information present in the environment.

Role of Norepinephrine in Alertness

  • Norepinephrine neurons originating in the locus coeruleus (LC) are crucial for alertness.
  • These neurons project widely and release norepinephrine from their axon terminals.
  • Activation of the LC by arousing stimuli alerts multiple brain areas simultaneously.
  • Norepinephrine enhances neuronal responses to environmental stimuli, increasing the signal-to-noise ratio by:
    • Strengthening the response to relevant stimuli (e.g., paw touch).
    • Reducing background neuronal activity.

Attention and Information Limits

  • Attention is essential for selecting information from a cluttered environment.
  • Human information processing is parallel up to a certain point, then becomes serial.
  • Allocation of attention determines which information is analyzed, thus limiting perception.
  • Inattentional blindness and change blindness illustrate the inability to process unattended information.

Selective Attention

  • Stimulus-driven/Bottom-up Attention: An automatic and involuntary process engaged by physically salient stimuli that "pop out".
  • Goal-directed/Top-down Attention: A serial process directed toward stimuli relevant to current goals; requires item-by-item search.

Feature-Integration Theory (Treisman & Gelade, 1980)

  • Visual search is easy and requires no attention when it involves a single feature (e.g., color, size, orientation).
  • Example: Finding a blue circle among other shapes.

Conjunction Search

  • Visual search becomes more difficult when conjunctions of features are involved (e.g., finding a red circle).
  • Integrating across multiple features (color, shape, orientation, size) requires directed, top-down attention.

Serial Search

  • Items are examined one at a time.
  • Search terminates when the target is found or all items have been examined.

Parallel vs. Serial Search

  • Parallel Search: Target has a distinct feature not present in distractors; set size does not impact timing.
  • Serial Search: Target shares features with distractors; time required to detect the target increases with set size.

Brain Regions Involved in Attention

  • Stimulus-driven Attention: Activates the temporoparietal junction (TPJ) and ventral frontal cortex (VFC).
  • Goal-directed Attention: Involves a network including the dorsolateral prefrontal cortex (dlPFC), intraparietal sulcus (IPS), and frontal eye fields (FEF).
  • Prefrontal and parietal regions are involved in selective attention, lateralized somewhat to the right hemisphere.
  • Attending to one side of a display activates the contralateral side of the primary visual cortex.

Disorders of Visual Attention

  • Neglect: Failure to acknowledge objects in the field contralateral to the lesion.
    • Patients may ignore one side of their body or external space.
  • Extinction: A milder form of neglect where a single stimulus in the contralateral visual field is detected, but not when another stimulus is simultaneously presented in the ipsilateral visual field.

Neuroanatomy of Neglect

  • Classically associated with lesions in the posterior parietal cortex, particularly the inferior parietal lobe (IPL) or temporoparietal junction (TPJ), typically in the right hemisphere.
  • Damage to prefrontal and subcortical regions like the thalamus and basal ganglia can also contribute to neglect.

Object-Based vs. Space-Based Neglect

  • Neglect can be object-based, where patients neglect the left side of an object regardless of its position in space.
  • Example: A patient with right neglect shown a rotating dumbbell continues to neglect the object that was initially on the right, even after it rotates to the left (Behrmann & Tipper, 1999).

Anosognosia

  • 10% of people with hemineglect have anosognosia, a denial of their deficit.

Frontal Lobe and Executive Control

  • Executive control is needed to inhibit attention to distractors.
  • Attentional Control: The ability to ignore less relevant stimuli while focusing on relevant ones.
  • Cocktail Party Effect: Example of attentional control where one can switch attention from a current conversation to another upon hearing their name in a noisy room.

Stroop Task

  • Used to examine resistance to distraction.
  • Participants are asked to say the color of the ink the word is printed in, while ignoring the word itself.
  • Compatible Condition: The word corresponds to its ink color.
  • Incompatible Condition: The word is printed in a conflicting ink color.

Brain Regions in Attentional Conflict Resolution

  • The anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (dlPFC) are activated during attentional conflict between competing sources of information, such as in the Stroop task.

Attention Deficit Hyperactivity Disorder (ADHD)

  • Symptoms include motor hyperactivity, inattention, and impulsiveness.
  • Symptoms are often most pronounced when the environment lacks sensory stimulation.

Effects of Stimulants in ADHD

  • Inhibit reuptake of dopamine by blocking the dopamine transporter (DAT).
  • Enhance the activity of neurotransmitter systems.
  • Reduce symptoms of ADHD.

Neural Activity in ADHD

  • Individuals without ADHD show greater activity in dopamine-rich regions of the prefrontal cortex and caudate during tasks like the go/nogo task.
  • Stimulants increase PFC and caudate activity and improve cognitive control in individuals with ADHD.

RECAP of Attention

  • Norepinephrine enhances alertness by increasing the sensitivity of sensory neurons.
  • Salient stimuli engage stimulus-driven or bottom-up attention, resulting in a pop-out effect.
  • Goal-directed attention is top-down and serial, requiring item-by-item search.
  • Damage to prefrontal and parietal regions can produce contralateral neglect (space/object).
  • ACC and dlPFC are important in detecting and resolving attentional conflict (attentional control in Stroop).
  • ADHD symptoms include hyperactivity, inattention, and impulsiveness; a predominant theory is a dopamine deficit, which stimulants address by inhibiting dopamine reuptake.

Working Memory

  • The ability to maintain and manipulate information over short periods of time (Baddeley, 1986).
  • Examples include calculating a tip, performing an N-Back Task, and completing a List Sorting Task.

Frontoparietal Circuitry in Working Memory

  • The frontoparietal network, including the dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex, is implicated in working memory capacity and development.

Development of Working Memory

  • Working memory performance for simple stimuli reaches a developmental asymptote by the teens.
  • Changes in working memory continue into the 20s, especially with complex stimuli involving increasing memory load and interference.

Neural Recruitment and Working Memory Improvement

  • Increased recruitment of DLPFC and parietal cortex is associated with developmental improvement in working memory.
  • DLPFC shows sustained activity during maintenance and resistance to distractors, which increases with age.

Delayed Saccade Task

  • Measures working memory ability.
    • Animal fixates on a point.
    • A visual cue appears briefly.
    • During a delay, the stimulus disappears, requiring the animal to hold its location in working memory.
    • The animal makes a saccade to the remembered location for a reward.
  • During the delay period, prefrontal cortical neurons become active.
  • Increase in delay-related persistent DLPFC neuronal firing and resistance to distractors with maturation.

Neuronal Mechanisms of Working Memory

  • Networks of working neurons are thought to excite one another through recurrent connections.
  • Excitatory neurotransmitters maintain the activity of other neurons in the network, allowing neuronal activity to reverberate back and forth.

Types of Connections

  • Recurrent Connections: Involve loops of signals back and forth between neurons, allowing them to remain active over time.
  • Divergent Connections: A small number of neurons broadcast to a large number of recipients.
  • Convergent Connections: Many neurons send signals to a few neurons.

Brain Areas and Memory

  • Brain areas active during both perception of, and memory for, an object include the fusiform gyrus (faces) and parahippocampal gyrus (places).
  • When remembering an item, the same brain regions are activated as when viewing that item (imagery).
  • Switching attentional focus from memory of a face to memory of a place activates the same prefrontal and parietal areas as when shifting and focusing attention to external stimuli.

RECAP of Working Memory

  • Norepinephrine enhances alertness by increasing the sensitivity of sensory neurons.
  • Salient stimuli engage stimulus-driven or bottom-up attention, resulting in a pop-out effect.
  • Goal-directed attention is top-down and serial, requiring item-by-item search.
  • Damage to prefrontal and parietal regions can produce contralateral neglect (space/object).
  • dlPFC and ACC are important in resolving attentional conflict (attentional control in Stroop).
  • ADHD symptoms include hyperactivity, inattention, and impulsiveness. A predominant theory is a dopamine deficit hypothesis given that stimulants inhibit reuptake of dopamine to enhance DA activity and reduce symptoms.
  • Working memory is the ability to maintain and manipulate information over short periods of time.
  • Neural correlates of WM include the dorsolateral PFC and posterior parietal cortex.
  • Dorsolateral PFC neurons remain active during the delay period when items are held in memory and involve recurrent projections. Sustained activity changes with development.
  • When remembering an item, activate the same brain regions as when viewing an item (imagery). When switching focus between items in memory, activate attentional frontoparietal regions.