Influences of baseline condition and task demand on the involvements of premotor cortex and primary motor cortex in action language comprehension: A meta-analysis study

Numerous studies find that premotor cortex and primary motor cortex are strongly activated during comprehension of action language. However, the findings are inconsistent across studies using different paradigms. The current meta-analysis study investigated how baseline conditions and task demands influence the observation on the involvements of premotor cortex and primary motor cortex. Twenty-one fMRI studies about action language comprehension were included and divided into different groups based on their baseline conditions and task demands. The contrast effects between action language comprehension and baseline were examined when (1) the baseline contained no linguistic information, (2) the baseline contained non-action semantic information; (3) the task was passive reading or listening; and (4) the task required making decisions and giving motor responses. We also examined the effect of one factor while controlling the other factor at a certain level. The results showed that regardless of task demand, comprehension of action language elicited strong activations in both premotor and primary motor cortex when baseline condition contained no linguistic information. However, when baseline conditions contained semantic information, only right primary motor cortex showed a strong effect. This result pattern was similar to that when tasks were passive. When tasks required making decisions and giving motor responses, the contrast between action language processing and low-level baselines indicated strong activations in premotor and primary motor cortex, but no significant effect was found when baseline contained semantic information. These results suggest that premotor cortex and primary motor cortex play different roles in action language comprehension. Primary motor cortex is involved in the semantic processing of action features, while premotor cortex is related to general linguistic processing. The interaction between baseline condition and task demand suggests that a combination of a passive task and a semantic baseline might be appropriate to investigate the role of premotor cortex and primary motor cortex in action language comprehension.