New findings support a mathematical model predicting that the slow, steady firing of neurons in the dorsolateral prefrontal cortex that maintains visual representations in working memory relies on a class of NMDA receptors known as NR2B receptors. Blocking these receptors abolished persistent firing among pyramidal Delay cells.

Earlier studies have shown these types of NMDA receptors are often altered in patients with schizophrenia. They also seem to be altered in Alzheimer’s patients. The findings suggest that this may be one cause of cognitive deficits in those with schizophrenia and Alzheimer’s.

Ketamine, an anesthetic often abused as a street drug, also blocked these receptors, explaining at least in part why ketamine abuse can produce schizophrenia-like symptoms.

https://www.futurity.org/health-medicine/brains-sketch-pad-goes-blank-in-schizophrenia/

[3323] Wang, M., Yang Y., Wang C-J., Gamo N. J., Jin L. E., Mazer J. A., et al.
(2013).  NMDA Receptors Subserve Persistent Neuronal Firing during Working Memory in Dorsolateral Prefrontal Cortex.
Neuron. 77(4), 736 - 749.