Neural representations of letters in human medial temporal lobe predict working memory response times

The medial temporal lobe (MTL) supports human memory and the structured representation of information, yet how it encodes complex content in working memory remains unclear. Here we recorded single-neuron activity from the MTL of 11 epilepsy patients performing a working memory task involving letter strings from a pool of 15 consonants. Using population-level decoding, we identified significant neural representations of 8 individual letters, stable across varying memory loads and trial types. Behaviorally, response time increased with set size, a pattern typically explained by a scanning process. We provide evidence for a complementary mechanism, in which letters with higher decoding accuracy corresponded to faster response times, linking MTL neural representations to memory strength. These findings suggest that MTL neurons encode complex information, and that such neural representations are associated with efficient verbal working memory performance.