  Statistical learning has been proposed as a mechanism to structure and
segment the continuous flow of information in several sensory modalities.
Previous studies proposed that the medial temporal lobe, and in particular the
hippocampus, may be crucial to parse the stream in the visual modality.
However, the involvement of the hippocampus in auditory statistical learning,
and specifically in speech segmentation is less clear. To explore the role of
the hippocampus in speech segmentation based on statistical learning, we
exposed seven pharmaco-resistant temporal lobe epilepsy patients to a
continuous stream of trisyllabic pseudowords and recorded intracranial
stereotaxic electro-encephalography (sEEG). We used frequency-tagging analysis
to quantify neuronal synchronization of the hippocampus and auditory regions to
the temporal structure of words and syllables of the stream. Results show that
while auditory regions highly respond to syllable frequency, the hippocampus
responds mostly to word frequency. These findings provide direct evidence of
the involvement of the hippocampus in speech segmentation process and suggest a
hierarchical organization of auditory information during speech processing.
