Establishing the functional connectivity of the frontotemporal network in pre-attentive change detection with Transcranial Magnetic Stimulation and event-related optical signal.

Current theories of pre-attentive deviant detection postulate that before the Superior Temporal Cortex (STC) detects a change, the Inferior Frontal Cortex (IFC) engages in stimulus analysis, which is particularly critical for ambiguous deviations (e.g., deviant preceded by a short train of standards). These theories rest on the assumption that IFC and STC are functionally connected, which has only been supported by correlational brain imaging studies. We examined this functional connectivity assumption by applying Transcranial Magnetic Stimulation (TMS) to disrupt IFC function, while measuring the later STC mismatch response with the event-related optical signal (EROS). EROS can localize brain activity in both spatial and temporal dimensions via measurement of optical property changes associated with neuronal activity, and is inert to the electromagnetic interference produced by TMS. Specifically, the STC mismatch response at 120-180 ms elicited by a deviant preceded by a short standard train when IFC TMS was applied at 80 ms was compared with the STC mismatch responses in temporal control (TMS with 200 ms delay), spatial control (sham TMS at vertex), auditory control (TMS pulse noise only), and cognitive control (deviant preceded by a long standard train) conditions. The STC mismatch response to deviants preceded by the short train was abolished by TMS of the IFC at 80 ms, while the STC responses remained intact in all other control conditions. These results confirm the involvement of the IFC in the STC mismatch response and support a functional connection between IFC and STC.

Detecting violation in abstract pitch patterns with mismatch negativity.

The human brain automatically extracts regularities embedded in environmental auditory events. This study investigated the extraction of abstract patterns by measuring mismatch negativity (MMN). Participants watched a silent subtitled movie and ignored a sequence of auditory events comprising frequent standards and rare deviants presented in the background. Tone triplets with varying pitch (first-order property) served as the auditory events. The pitch intervals (interval 1 and interval 2) between the tones in a triplet and the ratio of interval 1 and 2 were considered second- and third-order properties, respectively. Both second- and third-order properties of the standards were kept constant in the mixed patterns block, while only the third-order property was kept constant in the ratio pattern block. Four sets of tone triplets violating the interval and ratio patterns with different deviance levels were presented as deviants in both blocks, and subtracted with physically identical stimuli in a control block to isolate the MMNs. Interval and ratio pattern deviants elicited MMNs in the mixed patterns block while only ratio pattern deviants elicited MMNs in the ratio pattern block. Larger MMNs were elicited by large deviants as compared to small deviants. These results suggest that the change detection system is sensitive to the violation of both second- and third-order abstract patterns. In addition to regularities in the abstract properties of auditory events, regularities in the relationships between abstract properties can also be extracted. This ability plays an important role in music and language perception.