P1: Functional Brain Changes in SZ

Lecture by Virginia Penhune
Presented by Joseph (Jake) Shenker

Functional scans consist of voxels.
Voxel: A 3D pixel, it represents the smallest distinguishable box-shaped part of a 3D space in brain imaging.
Standard space means all voxels are positioned relatively the same across different brains, allowing for effective overlap of structural and functional scans.

Involves techniques such as PET or fMRI along with structural MRI to produce a combined image.

Measures blood flow through various parts of the brain by assessing changes in blood oxygenation.
Oxygen (O2) is transported via hemoglobin which is paramagnetic; this means its magnetic properties change when it is in different states:
- Oxygenated hemoglobin (to cells) vs. deoxygenated hemoglobin (away from cells).
The most active brain areas show the most significant changes in O2 levels, leading to a considerable contrast between deoxygenated and oxygenated hemoglobin.
BOLD (Blood Oxygen-Level Dependent) contrast is the most common measure of brain activity in fMRI.

Unlike PET scans, fMRI requires a comparative analysis between different conditions to generate a signal.
- Experiments typically involve comparisons with a baseline condition and an active condition or between two distinct groups.
Example: Brain activity in the visual cortex is monitored when a visual stimulus is turned on and off.

A task comparison method where brain activity is measured during two separate tasks that vary by only one cognitive component, enabling the isolation of brain activity related to that component.
Example: Specific brain regions engaged in color vision can be identified by contrasting conditions.

Ensure that test and baseline conditions are closely matched to avoid confounding variables.
Examine blood flow changes only in targeted regions pertinent to the task performance.
Correlate blood flow data with behavioral measures of task performance.
As part of study design, patient groups and control must be well matched in terms of demographics and cognitive levels.

Observations have shown similar activation in the auditory cortex for hallucinations as for real sounds.
Other studies demonstrate decreased activity in the auditory cortex during inner speech—essentially talking to oneself.
Concept Explanation:
- The similarity in activity patterns demonstrates that auditory hallucinations are processed similarly to external auditory stimuli.
- Thus, hallucinations can be perceived as real because the brain treats them as if they are external sounds.
Terminology:
  - H = hallucinations
  - S = speech
  - R = reversed speech
  - T = tones

When articulating our thoughts, the motor cortex sends signals to the auditory cortex (through corollary discharge or efference copy), which reduces its activity.
- This mechanism helps differentiate between one's own speech and sounds from external sources.
This corollary discharge also occurs when one merely imagines speaking.
For individuals with schizophrenia (SZ), the auditory cortex does not receive this internal sound reduction signal, leading to indistinguishable experiences of internal and external sounds.

A test of attention where subjects respond to displays on the screen:
- Standard CPT: Participants hit a key when the letter “X” appears, with varying numbers of “X” displayed.
- A-X CPT: Participants hit the key only when the letter “X” follows an “A” on the screen.
Results indicate that while simple tasks present no problems for those with SZ, more complex tasks like the A-X version prove challenging.

Research frequently reports decreased activity in the dorsolateral prefrontal cortex (DLPFC) in individuals with SZ.
- There is ongoing debate, as some studies do not show decreased DLPFC activity.

Study involved both short and long delay scenarios in the A-X CPT administered to first episode SZ patients who had never taken medication.
Controls exhibited similar DLPFC activity during short delay tasks compared to SZ patients.
Controls demonstrated greater DLPFC activity for long delays, which SZ patients failed to replicate.
- Interpretation: Attention and DLPFC functioning may remain adequate in SZ for easier tasks, but individuals with SZ cannot recruit additional cognitive resources as complexity elevates.
- May indicate that early-stage dysfunction in DLPFC may be less pronounced than in later stages of the disorder.

Study examined A-X CPT performances focusing on brain scans taken before and after errors (T5, T6 prior; T7, T8 after).
Both controls and SZ patients showed similar neural activity for correct responses on the task.
Controls exhibited increased activity in the anterior cingulate cortex (ACC) after making errors, unlike SZ patients who showed no such increase.
- Significance of ACC: It is crucial for error detection and correcting behavior.

Listen to part 2 of the pre-recorded lecture on functional brain changes during the next session.
Quiz 3 scheduled for Tuesday, March 17, and will be available on Moodle.
In-person class on Wednesday, March 18, will include a review of quiz 3 article by Hart et al., 2013.