Article 3: fMRI of inner speech in sz

Question 1

Their hypothesis was “Reduced auditory cortex activity in controls but not in people with SZ”. Describe the evidence supporting this hypothesis.

Answer 1

• Other studies showed this effect
• Based on the idea that there is faulty efference copy mechanism
• Auditory cortex active during hallucinations

Question 2

The other hypotheses were:
H: People with SZ have disrupted self monitoring that leads them to mistake inner speech for external speech, leading to hallucinations.
H: SZ would show decreased suppression of auditory regions during inner speech compared to CTLs

What was the evidence supporting this hypothesis?

Answer 2

• Auditory regions are active during hallucinations
• Similar activity in auditory regions for hallucinations and external sounds (Dierks in Lecture 10)
• Auditory regions active during inner speech in healthy controls
• SZ showed greater activity in auditory regions when imagining someone else speaking

Question 3

Why is activity in auditory cortex decreased during inner speech?

Answer 3

• When we speak, motor cortex lets auditory cortex know (corollary discharge or efference copy)
• This reduces activity in auditory cortex (lets us know that we are speaking, not someone else)
• This also happens when we just imagine speaking (inner speech or talking to ourselves)
• During inner speech, the cingulate cortex is becomes more active
  (Likely due to its role in action monitoring)

Question 4

Describe the stimuli and tasks used to compare internally and externally generated speech in the study. How did the experimenters know that patients and controls were complying with the inner speech task?

Answer 4

Stimuli: 24 neutral sentences, spoken by a adult female native English speaker
Two part trial:
Listen + Inner Speech (repeat silently) + press button when done
Listen + Listen

Baseline: silence
Comparisons:
Second half of the trial when people were either listening or repeating silently

They knew the participants were complying because they had to press a button after the cues, after they were done repeating the sentence to themselves.

Question 5

How did activity in auditory cortex (left superior temporal gyrus) differ for internally and externally generated speech between patients and controls? What differences were observed in the cingulate cortex?

Answer 5

The auditory cortex (left superior temporal gyrus):

For the listening trials both the healthy controls and the SZ patients showed an activation in the left superior temporal gyrus. What was concluded from this finding was that listening to verbal auditory cues is not impaired in patients with SZ.

The difference between groups in this region of the brain was found in the inner speech task. In healthy controls, the left superior temporal gyrus showed a greater decreased activation than patients with SZ. This findings served as evidence that in SZ patients there is a defective self-monitoring of inner speech. Because the left superior temporal gyrus remains activated during listening and inner speech.

The cingulate cortex:

During the inner speech tasks, healthy controls showed an increased in activation in the anterior cingulate cortex, however for the listening task they showed a decrease in activation. The SZ patients group did not show an increase activation for the ACC during the inner speech tasks. This finding was consistent with previous studies which showed that the ACC shows decreased activity during cognitive inhibition tasks.

Question 6

Taken together, what do the observed differences in brain activity in auditory regions and the cingulate cortex tell us about possible mechanisms underlying hallucination in SZ?

Answer 6

• SZ patients show reduced auditory suppression during inner speech&raquo_space; Evidence of a defective self-monitoring system.
• SZ patients show reduced engagement of the Cingulate (ACC) during inner speech. ACC is involved in self-monitoring of action &raquo_space; related to misattributions of inner speech as external (i.e., hallucinations)