The Role of the Left Inferior Frontal Gyrus in Introspection during Verbal Communication

Abstract

Conversation enables the sharing of our subjective experiences through verbalizing introspected thoughts and feelings. The mentalizing network represents introspection, and successful conversation is characterized by alignment through imitation mediated by the mirror neuron system (MNS). Therefore, we hypothesized that the interaction between the mentalizing network and MNS mediates the conversational exchange of introspection. To test this, we performed hyperscanning functional magnetic resonance imaging during structured real-time conversations between 19 pairs of healthy participants. The participants first evaluated their preference for and familiarity with a presented object and then disclosed it. The control was the object feature identification task. When contrasted with the control, the preference/familiarity evaluation phase activated the dorso-medial prefrontal cortex, anterior cingulate cortex, precuneus, left hippocampus, right cerebellum, and orbital portion of the left inferior frontal gyrus (IFG), which represents introspection. The left IFG was activated when the two participants' statements of introspection were mismatched during the disclosure. Disclosing introspection enhanced the functional connectivity of the left IFG with the bilateral superior temporal gyrus and primary motor cortex, representing the auditory MNS. Thus, the mentalizing system and MNS are hierarchically linked in the left IFG during a conversation, allowing for the sharing of introspection of the self and others.

Keywords: conversation; hyperscanning functional magnetic resonance imaging; inferior frontal gyrus; introspection; mentalizing network; superior temporal gyrus.

Figure 1

Time course of one trial in the (A) introspection task and (B) object feature identification task. The number in the upper left corner of the balloon indicates an example of the order of utterance. Brain activity was analyzed in the evaluation (red border) and disclosure (blue border) phases.

Figure 2

Brain activity during the evaluation phase of introspection (including both preference and familiarity judgments), contrasted with object feature identification (Contrast #3, Table 1).

Figure 3

Brain activity during the disclosure phase of introspection relative to object feature identification, irrespective of mismatch and match conditions (Contrast #11, Table 1) (cyan region); and introspection-specific mismatch as compared with object feature identification-related mismatch (Contrast #12, Table 1) (magenta region).

Figure 4

Mismatch-related brain activity, irrespective of introspection or object feature identification (Contrast #13, Table 1) (red region). Significant regions identified with psychophysiological interaction analysis with the left inferior frontal gyrus as the seed region (green region). Areas shown in yellow indicate an overlap between the two (red and green) parts.