Increased Glutamate/GABA+ Ratio in Social Disorganisation

Abstract

• Autism and schizophrenia share phenotypic traits termed Social Disorganisation (SD).
• Study investigates glutamate (excitatory) and GABA (inhibitory) concentrations in non-clinical samples with high and low SD.
• Participants:
  • 18 low SD
  • 19 high SD
  • Age: 18-40
• Method:
  • 1H-MRS used to measure glutamate and GABA+ concentrations in superior temporal (ST) voxels.
• Results:
  • Reduced GABA+ and increased glutamate/GABA+ ratio in right ST voxel for high SD.
  • Increased bilateral glutamate concentration in high SD group.

Introduction

• Overlap in autism and schizophrenia:
  • Shared traits identified in non-clinical populations.
  • SD phenotype involves negative and disorganised traits (schizotypal) and social/interpersonal difficulties (autistic).
• Neurochemical abnormalities:
  • Glutamate and GABA imbalances reported in both autism and schizophrenia.
  • Psychosocial dysfunction linked to excitation/inhibition imbalance.
  • Auditory processing deficits in both spectra linked to glutamate and GABA levels.

Method

Participants

• Ethics approval from Swinburne University.
• Participants completed an autism schizotypy questionnaire (ASQ).
• Exclusion criteria: current psychoactive medication, psychiatric history.

ASQ

• Comprised items from AQ, SPQ, and other scales.
• Factor analysis used to identify SD scores.

1H-MRS Protocol

• Imaging conducted using a 3T Siemens MRI system.
• Voxels positioned in left and right superior temporal gyrus.
• Utilized PRESS and MEGA-PRESS sequences for quantification.

Analysis

• TRACQUIN and Gannet toolkits used for glutamate and GABA+ analysis respectively.
• Statistical analysis conducted using R.

Results

• Significant right hemisphere glutamate/GABA+ ratio increase in high SD group.
• Overall increase in glutamate concentration in high SD group.
• Increased GABA+ in left hemisphere for high SD group.

Discussion

• Key Findings:
  • Increased glutamate/GABA+ ratio in high SD group suggests hyper-glutamatergia.
  • Reduced GABA+ in auditory processing areas may lead to cortical over-excitation.
• Implications:
  • Suggests neurochemical abnormalities are specific to spectrum phenotypes.
  • Highlights the need for trait-related assessments in research.

Conclusion

• Increased glutamate/GABA+ ratio in right hemisphere linked to Social Disorganisation.
• Findings indicate potential neurochemical basis for social and communication difficulties.
• Suggests future research should focus on glutamate and GABA+ systems in non-clinical samples.