Paul Greengard, an American neuroscientist whose quest to understand how brain cells communicate provided new insights into psychological diseases and earned him a Nobel Prize, and who used his entire $400,000 award to create an academic prize in memory of the mother he never knew, died on Saturday in Manhattan. He was 93.

His death was confirmed by Rockefeller University, where he had worked since 1983.

Dr. Greengard received the 2000 Nobel Prize in Physiology or Medicine with Dr. Arvid Carlsson of Sweden and Dr. Eric R. Kandel of the United States for independent discoveries related to the ways brain cells relay messages about movement, memory and mental states. Their discoveries offered new insights into disorders linked to errors in cell communication, such as Parkinson’s disease, schizophrenia, bipolar disorder and drug addiction.

Dr. Greengard’s research described how cells react to dopamine, an important chemical messenger in the brain. His work provided the underlying science for many antipsychotic drugs, which modulate the strength of chemical signals in the brain.

“Our work shows the details of how dopamine produces these effects — in other words, what’s wrong in these diseases and what can be done to correct them,” Dr. Greengard said.