Functional connections in the default language network
A default language network would be a neural network which is activated for each language task. If such a network could be described it would be interesting to define the functional connections of different brain regions in such a default network.
On approach to identify the default network for language is to analyze the low-frequency fluctuations of fMRI data collapsed over a number of language experiments using different stimuli and tasks. Such an analysis provides relevant information concerning the functional neuroanatomical basis of language since the experimental conditions in a given experiment only explain a small portion of the total variance, the larger portion is accounted for by the low frequency fluctuation (Lohmann et al., 2010).
For language experiments, this activation can be located in the perisylvian cortex. Since this activation pattern was only observed for language experiments and not for non-language experiments (Lohmann et al., 2010). This was shown in a low-frequency fluctuation analysis of fMRI data comparing data of four language experiments with those of two non-language experiments all conducted in the same laboratory. Within this default language network, a significant correlational connectivity was found between Broca’s area in the IFG and the posterior superior temporal lobe (Lohmann et al., 2010) (see Fig. 5).
To summarize it is already within the default language network, that there are functional connections between different language regions, independent of the different conditions induced by a given experimental condition. Therefore, the particular activation pattern reported for specific experimental conditions aiming to test semantic or syntactic processes as reported in the different language fMRI studies only represents a modulation of this default language network.
Figure 5: Functional connectivities between the language cortices within the default language network
Results of a conjunction analysis involving four language experiments corrected for multiple comparisons using FDR thresholded at P < 0.05. A: correlations with the seed region BA 44, B: correlations with the seed region in FOP. For each experiment, the correlations were r-to-z transformed to ensure Gaussianity and then subjected to a voxelwise t-test across subjects. The map shows the z values for the conjunction of all four language studies. The z values are color coded as indicated by the color bar. Figure legend is taken from Friederici, 2011 (Physiological Reviews, 91(4), 1357-1392).