Disorders of Attention and Memory Flashcards
How does visuospatial attention differ from “attention” in ADHD?
- visuospatial attention – selectively processing one physical location in space to the exclusion of others
- “attention” in Attention- Deficit/Hyperactivity Disorder: which is more related to executive function
Classic test of visuospatial attention
The Posner cueing task
The Posner cueing task - two trial types:
Two trial types:
* 1. Congruent
* 2. Incongruent. - cue comes first, in different location than target
Comparing reaction time across these two trial types allows us to study visuospatial attention at a particular location
TIMING after cue is presented
The Posner cueing task - two trial types:
- Early after cue is presented: facilitation for responding to a target at the location
- Later after cue is presented: delay for responding to a target at that location = “inhibition of return”
Key purpose of The Posner cueing task
Key point here: we can point our attention to particular locations, and this may or may not be where our eyes are looking
Real life examples: separating visuospatial attention from eye gaze
- Being socially appropriate
- Avoiding driving distractions
Contralateral Neglect
- Patients don’t realize their issues on the left side of the brain - similar to agnosognosia
- Also called hemispatial or unilateral neglect - pointing to the fact that this is happening on one side
Where do difficulties occur, relative to the lesion area?
Contralateral Neglect
- Deficits in reporting on objects in space that is opposite the lesion; a spatial bias for directing eye movements and actions towards into ipsilesional space
- Not explained by low level visual or motor problems; instead, the saliency of contralesional objects is affected (different from a hemianopia, for example)
Causes
Contralateral Neglect
Stroke (most common), trauma, Alzheimer’s
What side is most common?
Contralateral Neglect
- Almost always right-side damage leading to left-side neglect
- Commonly features anosognosia
Visual evidence examples
- Clock drawing
- Line cancellation
- Drawing
Cognitive/Functional Examples
- Eye movements
- Imagination: map drawing
- Visual judgements
- Line bisection: non-brain-damaged individuals show a slight bias to the left – pseudoneglect – because of the right hemisphere’s dominance in processing space
Areas of injury leading to neglect
All in right hemisphere. Three major cortical areas:
a) Inferior parietal lobe and temporo-parietal junction
b) Superior temporal gyrus
c) Ventral frontal cortex
Areas of injury leading to neglect - what do the 3 cortical areas give?
- Involved in spatial orienting
- This network is important for transforming signals from the eyes and body into spatial representations
- Damage to white-matter tracts connecting the three sites can also lead to neglect
Why is neglect so lateralized?
Thought that right parietal cortex represents both sides of space while left parietal cortex monitors only the right
DWI (diffusion-weighted imaging) show…
Why do subcortical injuries lead to neglect?
cortical injury
PWI (perfusion-weighted imaging) show…
Why do subcortical injuries lead to neglect?
areas of delayed blood flow
Cortical hypoperfusion predicts…
Why do subcortical injuries lead to neglect?
neglect (if in right hemisphere)
> Subcortical injuries lead to…
Why do subcortical injuries lead to neglect?
neglect to the extent that they affect blood flow to cortex
Types of neglect:
- Egocentric - neglecting everything to left of themselves
- Object-centered - neglecting each left half of the item
Recovery can include…
- Allesthesia
- Simultaneous extinction
- Spectrum of recovery
- Prismatic adaptation
Allesthesia
Recovery can include…
- Responding to stimuli on the neglected side as though they were on the non-neglected side
- Mislocating the stimulus (someone touching their left hand, allesthesia - able to detect that they are touched, but on their right hand)
Simultaneous Extinction
Recovery can include…
- Responding to stimuli on the neglected side unless both sides are stimulated simultaneously, then they only notice the ipsilateral stimulus
- The easily detected stimulus “extinguishes” detection of the other stimulus
Prismatic Adaptation
Recovery can include…
- The prism lenses shift the visual field to the right.
- The person’s motor system reaches for the shifted image, instead of the actual target.
- The visual system sends feedback to the motor system.
- With practice, the motor system adapts to the new visual coordinates.
Balint’s syndrome
Recovery can include…
- A severe disruption of attention based on a large region of brain damage
- Bilateral damage to parieto-occipital lobes (stroke, some dementias, some trauma)
- Primary sensory processing, language, memory and judgment intact
3 functions of Balint’s syndrome
- Oculomotor apraxia
- Optic ataxia
- Simultanagnosia
Simultanagnosia
Balint’s syndrome - 3 features
- Inability to perceive simultaneous objects or events in the visual field
- Constriction of the visual “window” of attention
Oculomotor Apraxia
Balint’s syndrome - 3 features
- “sticky fixation” or “psychic paralysis of gaze”
- Due to damage to saccade-planning areas in parietal cortex
- Optic ataxia
Balint’s syndrome - 3 features
makes it difficult to use visual cues to reach for objects
- Reaching errors, such as overshooting or undershooting a target
- Inability to correct ongoing movements when a target moves
Treatments
Balint’s syndrome
- no standard treatment program exists
- Coping strategies can help (e.g. practice dialing a phone) but neurological change is difficult or impossible because of the distribution of brain damage
Changes to visuospatial attention and other traits
- The space around our bodies is prioritized by the attention system = “peripersonal space” (PPS)
- Within PPS, line bisection performance is biased leftward, outside it is biased rightward
- A larger PPS is correlated with trait anxiety and claustrophobia
- A smaller PPS is correlated with autism and schizophrenia
MEMORY
Types of amnesia
- Retrograde: difficulty forming new memories after the onset of amnesia.
- Anterograde: retrograde amnesia is the inability to recall memories from before the event
Retrograde amnesia is more common for recent memories than older memories
Patient HM
- Bilateral medial temporal lobectomy to treat epilepsy
- Resulted in profound anterograde amnesia
Where were HM’s lesions?
- HM’s lesions shown on left side of images and intact on the right side (though his lesions were bilateral)
HM’s removed structures
- Removal of hippocampus, amygdala, and nearby cortex (highly connected to hippocampus)
PRE-HM memory research:
thought that memory was one, collective ability
HM - Initial memory test
Memory duration
- Repeating different sets of numbers
- HM had a normal digit span (normal is 5-7, HM’s was 6)
HM - Digit Span + 1 memory test
- numbers are all the same, just expanding the pattern
- Only able to recall 6-8 (low)
- impairment of long-term memory (LTM) with sparing of short-term (STM)
Outcomes from HM’s differing memory test scores
- The two types of memory must be supported by different brain mechanisms
- EX: HM’s removed tissue associated with LTM but not necessarily STM
2 Memory systems:
- Short-term memory (STM): A temporary storage system; sometimes equated with the concept of working memory; encode to LTM, unrehearsed info is lost
- Long-term memory (LTM): A more permanent store of information; retrieve from STM
Sensory memory
a brief, fleeting sensory store.
Sensory memory forms…
- Iconic memory (visual) ~1 sec
- Echoic memory (auditory) ~5-10 sec
How do LTMs become durable and permanent? (not just fall away eventually)
consolidation
Researchers believe that the process of consolidation is mediated by…
- The hippocampus
- …and that individual memories are stored diffusely throughout the cerebral cortex
- Sleep is important for this!
- The memory qualitatively changes - is this still the “same memory”?
Does HM have any form of LTM
YES - Still able to learn skilled movements (procedural memory), despite no memory of having done the task before
Explicit vs implicit memory
Improvement over time = intact procedural memory (implicit, non-declarative)
* procedural memory
* priming
* learning through classical conditioning
Lack of memory for the training sessions = deficit in episodic memory (explicit, declarative)
* semantic memory
* episodic memory
HM’s levels of episodic vs impaired memory
HM lacked episodic memory (personal events) and showed impaired semantic memory (general facts)
Distinction between these types of explicit memory is more clearly shown by the case of Kent Cochrane, patient KC
- Following a motorcycle accident, KC experienced diffuse damage including bilateral hippocampal damage
- Anterograde amnesia – could not form new memories for personal events
- However, continued to learn new information such as famous names and internet terms (= preserved semantic memory!
Results from priming:
- Enhanced identification of previously encountered (primed) stimuli, even if not explicitly remembered
- Shows that previous exposure to information/stimuli can improve memory or performance
Classical conditioning (another form of implicit LTM):
learning to associate two stimuli that co-occur (e.g., rat and loud noise, hand and pin)
Memory dysfunction: Korsakoff Syndrome
- Result of brain damage due to thiamine (vitamin B1) deficiency
- Often (but not always) due to heavy alcohol consumption
- Often (but not always) preceded by Wernicke’s encephalopathy – an acute brain reaction to lack of thiamine: confusion, abnormal eye movements, hypothermia, coordination problems, coma
Korsakoff Syndrome - types of amnesia
- Severe anterograde amnesia, mild retrograde amnesia – limited to explicit memory
- Often confabulate – report inaccurate stories about event (never say “I don’t know”)
Korsakoff Syndrome - damaged structures
- medial diencephalic structures (thalamus & hypothalamus)
- diffuse damage to cortex, hippocampus, cerebellum
Korsakoff Syndrome - treatment
- thiamine supplements + nutrition
- address alcohol use if relevant
SPLIT BRAIN
How are the hemispheres connected?
- Left and right hemispheres are connected by a few white-matter tracts
- We don’t struggle on only one side of the body - have the other side to assist
Which of the white-matter tracts is largest?
Corpus callosum
Brief history of split-brain research
any study involving the severing of the corpus callosum (can cut fibers, burn areas, etc.)
1940’s
Brief history of split-brain research
- Researchers show that epileptic discharge can spread from one hemisphere to another via corpus callosum in monkeys
- First limited callosotomy procedure in humans to control seizures in patients with intractable epilepsy (not successful)
1950’s
Brief history of split-brain research
- Roger Sperry & colleagues study split-brain rats, cats, and monkeys to assess each hemisphere separately (1981 Nobel Prize)
- Better understanding of how cortex is lateralized
1960’s
Brief history of split-brain research
- New, more complete commissurotomy performed, successfully controls epilepsy
- Adaptation of animal techniques for use in human patient
In a human, what can each hemisphere in the cortex do?
Each hemisphere sees only the contralateral visual field (with some midline overlap - where both see what’s directly in front of you)
What can the left hemisphere see?
- sees right visual field
- can control RIGHT hand
- speaks (typically)
What can the right hemisphere see?
- sees left visual field
- can control LEFT hand (LEFT HAND CAN ONLY DRAW)
With different hemispheres controlling different sides, what does this mean for split-brain patients?
- We can selectively “drop” visual information into each hemisphere of the split-brain patient if they maintain fixation
- Can test what each hemisphere knows - then test the hand
- EX: right hemisphere sees star, tries to get left hand to draw what they saw
- EX: left hemisphere sees square, tries to get patient to verbally say what they saw
Differing levels of split - “Knight” presented on LEFT
- Normal Brain: can see “knight”
- Partial Brain: has an idea in mind, but can’t quite identify it - “two fighters in a ring…ancient…”
- Complete Split: didn’t see any word
How does each hemisphere communicate touch?
- Each hemisphere feels touch input from the contralateral side of the body sensory input crosses at brainstem
- We can selectively “drop” touch information into each hemisphere of the split-brain patient if they don’t see it and don’t use cross-midline touch
- > Anomia for objects held in the left hand
NOT EVERYTHING IS SEPARATE IN THE BRAIN
- Eyes move together, and either hemisphere can control saccadic eye movements via lower structures
- By looking at task performance in split-brain patients, we can make inferences about cortical vs subcortical system
Non-cortical examples:
Responding to some types of stimuli is preserved even without the corpus callosum e.g., judging parallel lines, apparent motion
Visual search EXAMPLE
- Instruction: Find the dark circle
- In normal subjects, each distractor linearly adds to the search time
- In split-brain patients, adding distractors increases search time by half as much = each hemisphere searches “its” array in parallel
- However, the left hemisphere is more strategic than the right (e.g., immediately limit search to only dark items)
The left hemisphere as “interpreter” - SHOVEL AND CHICKEN EXAMPLE
Left hem says, “Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.”
Agenesis of the corpus callosum:
people born without a corpus callosum
- Can be complete or partial
- Language skills, IQ fairly normal (unless other abnormalities present)
- Surprisingly minimal “disconnection syndrome” compared to adult split-brain patients!
- Plasticity in children allows alternative cross-hemispheric pathways (e.g., anterior commissure) to be reinforced
- If the task requires very complex integration of information across hemispheres (e.g., compare visually complex shapes across the midline, fast) some impairment is seen
