Prefrontal responses to Stroop tasks in subjects with post-traumatic stress disorder assessed by functional near infrared spectroscopy Yennu et al 2016

Overview of the Study

  • Purpose: Investigate selective attention-related hemodynamic activity in the prefrontal cortex among veterans with PTSD compared to healthy controls using functional near-infrared spectroscopy (fNIRS).

  • Methodology: Utilized multichannel fNIRS to assess brain activity in 15 combat veterans with PTSD and 13 healthy controls during an incongruent Stroop task.

Background

  • Post-Traumatic Stress Disorder (PTSD):

    • An anxiety disorder following exposure to traumatic events (i.e., combat, sexual assault).

    • Symptoms: Re-experiencing trauma, hyperarousal, sleep disturbances, attention deficits, and cognitive dysfunction.

    • Lifetime prevalence in American adults is roughly 7.8%; 9-25% among war-zone veterans.

  • Neuropsychological Findings:

    • Previous studies indicate attentional deficits and cognitive dysfunction in PTSD, particularly correlating with frontal lobe activity.

    • Hyperactivation in limbic regions like amygdala and insula, coupled with hypoactivation in prefrontal areas.

Research Methodology

  • fNIRS Technique:

    • Non-invasive optical neuroimaging method measuring cerebral hemodynamics using near-infrared light.

    • Previous studies utilized fNIRS to assess cognitive processes in PTSD, supporting its feasibility in studying brain activity.

  • Stroop Task Description:

    • Involves color-word matching where the word meaning conflicts with the color of the text (incongruent trials).

    • Measures selective attention and processing speed under cognitive load.

Results Summary

Behavioral Measures

  • Both PTSD and control groups had longer reaction times for incongruent Stroop tasks (Stroop2) compared to neutral tasks (Stroop1) but no significant differences in reaction times were observed between the groups for either task. Both groups had 100% accuracy.

Hemodynamic Responses

  • Healthy Controls:

    • Showed significant activation in the left lateral prefrontal cortex (LPFC) during Stroop tasks compared to baseline readings.

    • HbO2 changes indicate responsiveness and cognitive flexibility when faced with Stroop interference.

  • PTSD Group:

    • Failed to activate the left LPFC during incongruent Stroop tasks and showed significant deactivations, particularly during Stroop2, indicating cognitive processing difficulties.

    • Nine channels indicated significantly reduced HbO2 compared to controls, particularly in areas related to inhibitory control (VLPFC and DLPFC).

Key Findings

  1. PTSD subjects exhibited difficulty in overcoming Stroop interference, as reflected by reduced prefrontal activation in managing cognitive load.

  2. A significant negative correlation between reaction times and hemodynamic responses in left DLPFC was observed exclusively in the PTSD group during incongruent tasks, indicating impaired cognitive control.

  3. Overall, fNIRS proved to be a viable method to understand selective attention deficits in PTSD.

Experimental Observations

  • Observation 1: Healthy controls activated left pars opercularis during Stroop2 tasks, whereas PTSD subjects showed no significant activation.

  • Observation 2: Deactivation patterns in both groups indicated cognitive load was not effectively managed in PTSD patients.

  • Observation 3: Significant differences in hemodynamic response between the two groups during the incongruent task suggest distinct underlying pathophysiological mechanisms in PTSD.

Limitations and Future Directions

  • The lack of significant activation in the neutral task (Stroop1) shows it was perhaps too easy, suggesting future studies should use more complex tasks.

  • Potential confounding variables such as comorbid conditions among PTSD subjects and limited cortical regions covered by fNIRS.

  • Emphasis on developing more challenging Stroop paradigms for clearer contrasts in processing between PTSD and healthy subjects.

Conclusion

  • The study validates the use of fNIRS in mapping cognitive dysfunction in PTSD, providing insights into how PTSD affects cognitive processes, particularly in tasks requiring selective attention and inhibitory control. Further studies could enhance treatment strategies and interventions for affected individuals.