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Transcript

Latent Inhibition in Schizophrenia

Neal R. Swerdlow, David L. Braff, Heidi Hartston, William Perry, & Mark A. Geyer

Univeristy of California, San Diego; Department of Psychiatry

The Basics

Latent Inhibition... What's that?!

The scientific definition: The retarded acquisition of a conditioned response that occurs if the subject being tested is preexposed to the to-be-conditioned stimulus (CS) without the paired unconditioned stimulus (UCS).

HUH?!!?

The layman definition: when a person "ignores" a repetitive, irrelevant neutral stimulus that doesn't predict a, or relate to, an important event (until it is important).

How does latent inhibition relate to schizophrenia?

This is what the researchers set out to investigate.

Based on clinical observations:

  • Individuals with schizophrenia have a difficult time gating irrelevant stimuli from awareness

Due to preexposure and lack of latent inhibition, schizophrenics should be able to more quickly identify conditioned (former neutral stimuli)

Discussion...

1. Schizophrenia patients required more trials

than did control subjects in identifying the conditioned stimulus even with preexposure (criterion).

2. Auditory task was not replicated and did not prove significant, but that could be due to:

  • British accent on tape
  • testing conditions can't be reproduced perfectly

3. Problems with this research compared to previous research:

  • design (construct validity)
  • small sample size
  • different patient population
  • confounding medications

The Results

The Stats

In the auditory task: there was a significant difference in overall task performance between control and schizophrenic groups (Z=2.28, p<0.05).

In the visual task (considered to be easier): there was no significant difference detected between control and schizophrenic groups in overall task performance. However, preexposure had a significant effect on both groups.

Retrospectively, in comparing schizophrenics that smoked to those that did not, there was no significant difference in latent inhibition.

Works Cited

Braff, D.L, Geyer, M.A, Hartston, H., Perry, W., & Swerdlow N.R. (1996).

Latent inhibition in schizophrenia. Schizophrenia Research. 20. 91-103.

Tracey Axisa and the psych gang. (2010). Latent inhibition. Retrieved from YouTube.

Auditory latent inhibition

What the researchers knew:

Preexposure phase: Subjects fitted with earphones and instructed

to listen to a series of nonsense syllables, choose one, and count the number of times it was repeated.

  • List of 30 nonsense syllables repeated 5x with 1-2 seconds between
  • For half of each group (control and experiment), a burst of white noise occurred at random times throughout the trial
  • Immediately after the trial period (audiotape) ended, subjects were asked to report which syllable they chose and how many times it was repeated. (subjects that reported > or = 20 presented were excluded from analysis)

  • Schizophrenia patients with deficient latent inhibition are able to learn an association faster than expected based on their baseline (no preexposure to stimuli)

  • Latent inhibition is sensitive in rats based on early developmental influences

  • Studies on the neural circuits in rats yields important information about neural dysfunction in humans. Also allows for identification of specific brain regions involved.

Test Phase: All subjects sat in front of an electronic board and were presented with a box with a red button under their right hand. Instructed that they would hear various sounds, but certain sounds would result in the number on board increasing. Their job was to figure when the number would increase and indicate that by pressing the red button.

  • Recording identical to the one heard during preexposure phase was played
  • The number on the board increased at the end of the white noise distraction stimuli
  • Correct responses were counted if the subject pressed the button during white noise.

Visual latent inhibition

*Those subjects that did not participate in the

auditory task participated in the visual task.

The Method

Preexposure phase: Eight geometric designs were presented on a screen to subjects who were asked to choose one design, then count the number of times that it appeared.

  • Designs shown for 1 second in psuedorandom order
  • For half of each group (control and experiment), a solid square shape (not one of the geometric designs) was presented.
  • Immediately after the trial period ended, a tone sounded to indicate the end of the trial, and subjects were asked to report which design they chose, and the number of presentations of that design. (subjects that reported > or = 10 presented were excluded from analysis)

  • 180 total subjects
  • 107 control
  • 42 male, 65 female
  • 73 schizophrenics
  • 49 male, 24 female
  • 49 paranoid schizophrenic
  • 16 undifferentiated schizophrenic
  • 10 disorganized schizophrenic
  • 1 catatonic schizophrenic
  • 1 psychosis, not otherwise specified
  • 77.2% smokers

(smoking status was assessed retrospectively)

Two experiments conducted:

  • Auditory latent inhibition (replication)
  • Visual latent inhibition (extension)

Test phase: All subjects sat in front of a screen that would again show the geometric designs, but would also show an 'X'. Instructed that something on the screen would signal the 'X' to move from the center to the top of the screen then back again. Their job was to figure out what made the 'X' move and indicate this by pressing the 'shift' key on a keyboard immediately

before the 'X' moved.

  • Design presentation that was shown identical to preexposure phase
  • The 'X' moved 2.5 seconds after the solid square distraction was presented
  • Correct responses were counted if the subject pressed the 'shift'

key in the 2.5 second interval between presentation and

movement of 'X'.

The Experiment

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