Inferior frontal gyrus

The left opercular part of the inferior frontal gyrus is a part of the articulatory network involved in motor syllable programs. The articulatory network also contains the premotor cortex, and the anterior insula. These areas are interrelated but have specific functions in speech comprehension and production. The articulatory network acts mostly when the vocal tract moves to produce syllables. The pars opercularis acts indirectly through the motor cortex to control the motor aspect of speech production, and codes motor programs for this system, while the auditory cortex (via the temporoparietal junction in the lateral sulcus (Sylvian fissure) houses a series of sensory targets. Together, these areas function as a sensory-motor loop for syllable information coding.

In a study conducted comparing phonological and arithmetic processing and the involvement of different sections of the inferior frontal gyrus and angular gyrus, cortical activation for phonology, subtraction, and multiplication tasks was compared. The predetermined language-calculation network was limited to the left inferior frontal gyrus, angular gyrus, superior parietal lobule, and the horizontal portion of the intraparietal sulcus. The results were significant to support that there was a pattern of left lateralization for each of these tasks all activating the Perisylvian fissure network, with some general localized areas for phonology and arithmetic. It was supported that phonology activated the pars opercularis (BA44), and anterior angular gyrus, multiplication mainly implicated the pars triangularis (BA45), and the posterior angular gyrus. These systems are activated through similar neuronal processes but independently placed along the network.

Most language processing takes place in Broca's area usually in the left hemisphere.[9] Damage to this region often results in a type of non-fluent aphasia known as Broca's aphasia. Broca's area is made up of the pars opercularis and the pars triangularis, both of which contribute to verbal fluency, but each has its own specific contribution. The pars opercularis (BA44) is involved in language production and phonological processing due to its connections with motor areas of the mouth and tongue. The pars triangularis (BA45) is involved in semantic processing. Characteristics of Broca's aphasia include agrammatic speech, relatively good language comprehension, poor repetition, and difficulty speaking mostly uttering short sentences made up mostly of nouns. The left IFG has also been suggested to play a role in inhibitory processes, including the tendency to inhibit learning from undesirable information. For example, transcranial magnetic stimulation to the left IFG has been shown to release such inhibition, increasing the ability to learn from undesirable information.[10]

The right opercular part of the IFG, (BA44) has been implicated in go/no go tasks.[11] In these tasks, the participant encounters a preliminary task (for instance repeatedly pressing a button), and then must halt this task whenever a "no go" signal is presented, ultimately measuring a level of impulse control through inhibition of a prepotent response. It seems that the same area is also implicated in risk aversion: a study found that higher risk aversion correlated with higher activity at IFG.[12] This might be explained as an inhibition signal to accept a risky option. Disruption of activity of this area with transcranial direct-current stimulation (tDCS) leads to change in risk attitudes, as behaviorally demonstrated by choices over risky outcomes.[13][14]