Functional imaging of the thalamus in language

Abstract

Herein, the literature regarding functional imaging of the thalamus during language tasks is reviewed. Fifty studies met criteria for analysis. Two of the most common task paradigms associated with thalamic activation were generative tasks (e.g. word or sentence generation) and naming, though activation was also seen in tasks that involve lexical decision, reading and working memory. Typically, thalamic activation was seen bilaterally, left greater than right, along with activation in frontal and temporal cortical regions. Thalamic activation was seen with perceptually challenging tasks, though few studies rigorously correlated thalamic activation with measures of attention or task difficulty. The peaks of activation loci were seen in virtually all thalamic regions, with a bias towards left-sided and midline activation. These analyses suggest that the thalamus may be involved in processes that involve manipulations of lexical information, but point to the need for more systematic study of the thalamus using language tasks.

Fig. 1

Compilation of center of activation foci taken from Talairach and Tournoux coordinates (either given in original publications or transformed from MNI coordinates). Two axial sections are shown. (A) Taken from 2.7 mm superior–inferior (base image reproduced from Morel (2007)). (B) Taken from 8.1 mm superior–inferior. Each study is represented by a different symbol. (C) Histogram of number of activation loci within each 10 mm of midline in the medio-lateral dimension. Where activation foci fell on the border, half a locus was placed into each of the neighboring bins. Abbreviations: A = anterior, P = posterior, M = medial, L = lateral, AM = anteromedial nucleus, AV = anteroventral nucleus, Cd = caudate nucleus, CeM = central medial nucleus, CL = centrolateral nucleus, CM = center median nucleus, GPe = globus pallidus externa, Hb = habenular nucleus, ic = internal capsule, Li = limitans nucleus, LP = lateral posterior nucleus, MDmc = mediodorsal nucleus, magnocellular division, MDpc = mediodorsal nucleus, parvocellular division, MDpl = mediodorsal nucleus, paralamellar division, mtt = mammillothalamic tract, Pf = parafascicular nucleus, PuA = anterior pulvinar, PuL = lateral pulvinar, PuM = medial pulvinar, PuT = putamen, Pv = paraventricular, R = thalamic reticular nucleus, sm = stria medullaris, VAmc = Ventral anterior nucleus, magnocellular, VApc = Ventral anterior nucleus, parvocellular, VLa = ventrolateral anterior, VLpd = ventrolateral posterior nucleus, dorsal division, VLpv = ventrolateral posterior nucleus, ventral division, VM = ventromedial, VPLa = ventral posterior nucleus, anterior division, VPLp = ventral posterior nucleus, posterior division. Anatomical image reproduced with permission from Informa Healthcare.

Fig. 2

Foci taken from Fig. 1, color coded by nature of the task. All foci were collapsed onto a single superior–inferior plane. Units are in millimeters.