Sensory Gating Flashcards
What is sensory gating?
Sensory gating is the ability to respond when a stimulus change, and the ability to inhibit incoming redundant input.
Which ERP component is associated with sensory gating in?
Mismatch Negativity (MMN). The MMN is a negative ERP component elicited automatically and detected even in the absence of attention. It reflects the difference in an incoming stimulus from the sensory memory trace of the stimuli MMN is a derived concept. It is calculated by subtracting the ERP to standard from the ERP to deviant
How may the new, incoming stimulus deviate from the standard stimuli?
- Pitch
- Duration
- Intensity
What are the two subcomponents of the MMN?
- Supratemporal component (auditory Cx) - positive, rarely examine
- Frontal component (frontal Cx) - negative, main MMN
Where is the MMN?
MMN has frontocentral topography and is largest at Fz. Source mapping shows frontal MMN preceded by a temporal subcomponent.
List the tasks used to generate an MMN.
- Oddball paradigm: most commonly used paradigm where presentation of sequences of repetitive stimuli are frequently interrupted by a deviant stimuli
- Roving paradigm – using trains. 1st stimulus is deviant to last train and compared to standards T1-T2 (S and D are the same perceptually)
List the task considerations for an MMN task.
- Inter-stimulus interval (ISI), 500ms shorter ISI, decreased MMN
- Probability of the deviant stimulus 5-20%
- Number of trials >150 deviants, signal to noise
- Attention – ignore tones, attention controlled by other visual stimuli
What is involved in the EEG analysis of the MMN?
- Reference data separately to mastoids and to nose
- 1-20Hz bandpass filter
- Epoch data to standard stimuli and to deviant stimuli
- Subtract standard from deviant to give MMN
Describe the relationship between the MMN and the NDMA receptor.
It is thought that the MMN may reflect function of NDMA-type glutamate receptors. NDMA receptor antagonists (blockers) reduce MMN.
What are the two underlying theories of the MMN?
Sensory Memory Trace Mismatch Interpretation
- Repeating standard sound, followed by a deviant
o MMN amplitude increases with decreases probability of the deviant stimulus
o MMN amplitude increases and latency decreases with perceptual difference between deviant and stimulus
o MMN elicited in absence of attention (book, movie) and in the presence of attention to deviants (but overlap with attention ERPs)
- MMN elicited when the deviant encounters a strong memory trace
o Not by infrequent sounds in the absence of a frequent sound
o Not by sound pairs when all possible combinations (AB, BA, AA, BB) are equi-probable
Regularity-violation interpretation
- Suggests that the paradigms that are used are invalid. Focuses on relationships between sound.
- Complex, ecologically valid paradigms
- Standard – not a repetitive sound, rather regular relationship between sounds
- Deviant is a regularity violation
- In oddball, the repetition of the same standard tone = regularity representation (rather than sensory memory trace for that sound)
So perhaps the MMN represents an adaptive mechanism where new info requires an adaptive response. MMN might also signal the need to update pre-existing predictive models.
What are the real-life applications of the MMN?
Research has looked in the MMN being an endophenotype for psychological/psychiatric disorders (measureable trait connecting the genetic blueprint to the psychiatric disorder)
Schizophrenia
- MMN is reduced in schizophrenia and also attenuated in relatives. Studies found different patterns based on the duration of the illness
- Prodromal (started showing symptoms but haven’t yet been fully affected) – duration MMN
- Chronic – reductions in frequency MMN
- Decreased duration MMN in first-episode psychosis EP & ultra-high risk individuals
Cannabis
- One study examined acute administration of THC and effect on MMN
- THC alone was not observed to have an effect on MMN
- Only slight differences were found for frequency
- Reduced MMN for long term cannabis users
- Also, relationships between duration MMN (reduced with an increased cannabis use over the years) and duration of daily cannabis use
- Residual effects – both short term and long-term users both showed MMN
- Long term users had attenuated duration MMN, duration MMN correlated with duration of daily use
- Duration MMN only at trend level, so not significant but close
- Acute effects of cannabinoids on MMN – THC alone, CBD alone, THC+CBD high and low combination, placebo
Coma
- MMN can be recorded without attention
- Predictor of recovery from coma
o Measuring perceptual processing capabilities
o MMN present – 100% likelihood of wakening
o MMN absent – 84% likelihood on non-awakening
Aging
- MMN reduces with age
- Negative correlation with working memory and MMN
Which ERP component reflects sensory gating out?
P50 is a positive-going ERP component. Represents inhibition of irrelevant sensory input, protects brain from flood of unnecessary information
How is the P50 measured?
Paired-click paradigm (PCP) – click stimuli (tones) 1ms duration. SOA 500ms, IPI typically 8-10 seconds
Attention
- Active: count 25 pairs of clicks, press button
- Passive: no task
- Attention may affect groups different – attend to S2, patients with Sz and controls. Increased P50 S1 relative to passive condition. Decreased differences between groups (no group effect)
How is the P50 quantified?
P50 amplitude to S1 and S2 at Cz - peak to peak method, baseline to peak
P50 ratio: (P50-to-S1)/(P50-to-S2)
- A large ratio indicates poor gating
- A small ratio, S2 suppressed, indicates good gating
P50 difference score: (P50-to-S1) - (P50-to-S2)
- Larger difference scores = effective suppression, protective – not processing stimuli we don’t need to
What are the real-life applications of the P50?
Schizophrenia
- Don’t see that level of suppression as you do for people with schizophrenia
- Patients with schizophrenia exhibit worse sensory gating
- Patterson et al. (2006) – P50 ratios were larger in schizophrenic patients. Effect is independent of filter settings, gender, age and analysis
- May be an endophenotype for SZ so check relatives. Intermediate P50 ratios in relatives. Significant difference between controls and those with schizophrenia. Relatives were halfway between controls and relatives with schizophrenia. Could be used to understand the change from a genotype to a phenotype. That is, having the gene but not developing it
- Medication effects – larger reduction in P50 ratios for 1st vs. 2nd generation antipsychotics
o First generation antipsychotic: P50 ratios medicated were approximately equal to unmedicated patients
o Second generation antipsychotics: responders to Clozapine showed improved gating, non-responders did not. With prolonged treatment clinically stable participants show reduced P50 ratios, improved gating associated with lower BRPS scores
Cannabis use
- No difference in any P50 measures, but some correlations between size of suppression and duration of regular cannabis use
- Difference based on use-durations vs. controls. Were differences between short and long-term users. P50 ratio was increased in long-term users, no differences for short-term users.
- Larger P50 ratios in ex-users
- Poorer P50 gating correlated with prior duration of cannabis use
- At UOW: investigating acute effect of THC and CBD on P50. Further extent to which P50/MMN are attenuated in family member of individuals who smoke cannabis regularly
PTSD
- Results from life threatening trauma
- Associated with perceptual and cognitive dysfunction
- There is something about the development of that disorder and suppression abilities
- Study with 20 PTSD, 20 suffered trauma but no PTSD, 20 non-PTSD. Poorer gating in PTSD, non-PTSD were equal to the controls. Results unchanged after excluding smokers, improved gating correlated with quality of life index
Panic Disorder
- P50 ratios were different between controls and panic, control and schizophrenia. No difference between panic and schizophrenia. Sensory gating decreased PD.
