Schizophrenia is a major public health problem associated with cognitive deficits, such as short and long term memory, executive functioning, attention and speed of processing that are amongst the strongest predictors of impaired functional outcome. In addition, schizophrenia patients show reduced "plasticity", defined as reduced learning.

D-serine is a naturally occurring activator of the N-methyl-d-aspartate-type glutamate receptors (NMDAR) in the brain, and this project will assess the optimal dose of D-serine treatment over three sessions of a program designed to measure auditory plasticity.

Schizophrenia (Sz) is a major public health problem associated with core cognitive deficits that are amongst the strongest predictors of impaired functional outcome. In addition, Sz patients show reduced cortical neuroplasticity, defined as reduced learning during training on exercises that place implicit, increasing demands on early auditory information processing. As improved auditory processing can facilitate gains in those cognitive processes that are more proximal to daily functioning (e.g., verbal memory, executive functioning), enhancing neuroplasticity for better auditory processing represents an unmet clinical need and a rate-limiting first step prior to remediating cognition and overall function.

As supported by recently published data and review, the study proposes that localized N-methyl-D-aspartate-type glutamate receptor (NMDAR) dysfunction leads to impaired auditory neuroplasticity, which in turn leads to impaired cognition. Over recent years, NMDAR glycine site agonists have increasingly been shown to facilitate neuroplasticity in both Sz and healthy volunteers.

D-serine is a NMDAR modulator that when combined with neuroplasticity-based auditory remediation, leads to highly significant, acute improvement in both auditory plasticity and the early auditory processing measures mismatch negativity (MMN) and theta intertrial coherence (theta). Both MMN and theta-ITC are sensitive measures of functional target engagement of both NMDAR agonism and auditory remediation. In a preliminary study, plasticity correlated with reading and working memory, suggesting plasticity improvements are predictive of functionally relevant outcomes. While D-serine appears to be efficacious for neuroplasticity enhancement and target engagement in a dose dependent manner, the optimal dose remains an open question, as does the ability of combined D-serine + neuroplasticity-based auditory remediation to produce sustained, functional improvement. This study utilizes the Early Stage Testing of Pharmacologic or Device-based Interventions for the Treatment of Mental Disorders (R61/R33): RFA-MH-17-702.

The ultimate goal of this study is to enhance efficacy and efficiency of auditory cognitive remediation by augmenting with D-serine. This study will confirm target engagement, pharmacodynamics, functional relationships and the optimal dose (80 vs.100 vs. 120 mg/kg, IND: 122821) of D-serine treatment combined with 3 sessions of our auditory remediation program. As previously, D-serine will be given 30 minutes before sessions, allowing for auditory remediation during peak serum levels and a pharmacodynamic assessment. Successful completion is defined by ≥moderate effect size change in auditory plasticity, MMN and theta, plus a moderate effect size correlation with functionally relevant cognitive measures ("auditory cognition") without safety issues. Successful completion of this study will pave the way for a larger, definitive study pairing D-serine with auditory remediation or testing alternative dose intervals (1x vs. 2x week). In addition to testing a potentially viable treatment, this project will stimulate industry to utilize this methodology to assess the efficacy of novel NMDAR modulators, using D-serine as a "gold-standard."

Inclusion Criteria:

1. Age between 18 and 50

2. DSM-V diagnosis of schizophrenia or schizoaffective disorder

3. Willing to provide informed consent

4. Auditory Cognitive impairment demonstrated by:

   a .MCCB composite domain score less than or equal to 0.5 standard deviation below normal (T score less than or equal to 45) b. And at least one of the following:

   • MCCB verbal memory domain score less than or equal to 0.5 standard deviation below normal (T score less than or equal to 45)
   • Tone matching score of less than or equal to 77.7%

5. Clinically stable for 2 months (CGI less than or equal to 4)

6. Moderate or lower cognitive disorganization (PANSS P2 less than or equal to 4)

7. Medically stable for study participation

8. Willing to use qualified methods of contraception for the study duration and up to 2 months after its end

9. Fluent English speaker

10. Normal hearing

11. Visual acuity corrected to 20/30

12. An estimated Glomerular Filtration Rate (GFR) greater than or equal to 60

13. Taking an antipsychotic medication other than clozapine at a stable dose for at least 4 weeks

14. Judged clinically not to be at significant suicide or violence risk

Exclusion Criteria:

1. ECG abnormality that is clinically significant in the context of study participation in the opinion of the study cardiologist
2. Current clozapine use
3. Presence of positive history of unstable significant medical or neurological illness
4. Positive toxicology screen for any substances of abuse
5. Substance use disorder (excluding nicotine) within last 60 days
6. Pregnant women or women of child-bearing potential, who are either not surgically-sterile or for outpatients, using appropriate methods of birth control. Women of childbearing potential must have a negative serum -hCG pregnancy test at every visit.
7. Participation in study of investigational medication/device within 4 weeks
8. Subjects with suicidal ideation with intent or plan (indicated by affirmative answers to items 4 or 5 of the Suicidal Ideation section of the baseline C-SSRS) in the 6 months prior to screening or subjects who represent a significant risk of suicide in the opinion of the investigator Section

3 weeks