Human Superior Temporal Gyrus Organization of Spectrotemporal Modulation Tuning Derived from Speech Stimuli

The human superior temporal gyrus (STG) is critical for speech perception, yet the organization of spectrotemporal processing of speech within the STG is not well understood. Here, to characterize the spatial organization of spectrotemporal processing of speech across human STG, we use high-density cortical surface field potential recordings while participants listened to natural continuous speech. While synthetic broad-band stimuli did not yield sustained activation of the STG, spectrotemporal receptive fields could be reconstructed from vigorous responses to speech stimuli. We find that the human STG displays a robust anterior–posterior spatial distribution of spectrotemporal tuning in which the posterior STG is tuned for temporally fast varying speech sounds that have relatively constant energy across the frequency axis (low spectral modulation) while the anterior STG is tuned for temporally slow varying speech sounds that have a high degree of spectral variation across the frequency axis (high spectral modulation). This work illustrates organization of spectrotemporal processing in the human STG, and illuminates processing of ethologically relevant speech signals in a region of the brain specialized for speech perception.

Successful memory formation is driven by contextual encoding in the core memory network

We assessed the electrophysiological correlates of associative processing by comparing intracranially recorded EEG activity during the encoding of items that were subsequently recalled and clustered; recalled and not clustered; or not recalled. We found that high frequency activity (HFA) in left prefrontal cortex, left temporal cortex and hippocampus increased during the encoding of subsequently recalled items. Critically, the magnitude of this effect was largest for those recalled items that were also subsequently clustered.

Encoding speech sequence probability in human temporal cortex

In my quick first pass, this seems like a nice demonstration of phonotactic probability (likelihood of auditory transitions) being reflected in superior temporal gyrus. Though, the effects of lexicality suggests something more than pure transition probability is going on here.

Transition probability first negatively modulated neural responses, followed by positive modulation of neural responses, consistent with coordinated predictive and retrospective recognition processes, respectively. Furthermore, transition probability encoding was different for real English words compared with nonwords, providing evidence for online interactions with high-order linguistic knowledge.