Part II Experimental Investigation
7. An fMRI study on processing of proper names
7.2.2 Visual results
Word-category-specific differences were observed in the contrasts to the control (Arabic words) (see Figure 23) and in the contrasts between word categories (proper names vs. common nouns and vice versa). When compared with Arabic words, personal names mainly evoked activation in the left frontal area. Common nouns involved the ventral frontal cortex and the central sulcus. Geographical names engaged predominantly the left middle temporal cortex. When proper names and common nouns were compared with each other, proper names, including personal names and geographical names, showed significant activation in the frontal lobe including the frontal eye fields and premotor areas, whereas common nouns yielded significant activation in the left posterior temporal cortex and temporo-parietal areas. The following sections describe the results in more details.
Activation for different word categories
Anatomical visualization of these three word categories relative to baseline Arabic words is shown in Figure 23. Relative to Arabic words, reading personal names evoked activation mainly in left inferior frontal gyrus (BA 46, 47). Furthermore, activity in bilateral cuneus and right precuneus (BA 7) was observed. There was no activation in the temporal lobe.
Reading common nouns, instead, was associated with activations in bilateral superior temporal gyri (BA 22), left middle temporal gyrus (BA 21) and left fusiform gyrus (BA 19). Furthermore, activation in the bilateral anterior frontal area and central sulcus was revealed. Parietal activation for common nouns included bilateral inferior parietal lobules (BA 40) and left postcentral gyrus. Other involved areas were caudate, clustrum, thalamus in the right hemisphere; parahippocampal gyrus, insula in the left hemisphere. Activation was also demonstrated bilaterally in the anterior cingulates, lentiform nulceus and cingulate gyri.
Reading geographical names caused more stimulation in right orbitofrontal area (BA 11) and right dorsolateral area (BA 9, 10). Further frontal activation included right cingulate gyrus (BA 32) and left precentral gyrus (BA 6). Regarding the temporal lobe, the involved area in the left hemisphere was larger than the right (a small cluster in the superior temporal gyrus). Furthermore, bilateral activation in the inferior parietal lobules was also observed.
R L
Figure 23: Brain activation maps for (A) personal names vs. Arabic words (B) common nouns vs. Arabic words (C) geographical names vs. Arabic words in the visual experiment.
Dissociation between proper names and common nouns Characteristics of proper names
Personal names, compared with common nouns, significantly activated bilateral middle frontal gyri (BA 8, 46 ), superior frontal gyri (BA 9, 10) and right paracentral lobule (BA 5) and right precentral gyrus (BA 4). Activation in the temporal lobe was only found in the right temporo-occipital junction, namely in middle temporal gyrus (BA 21) and superior temporal gyrus (BA 22). Parietal activation was also right dominated, main activation patterns were found in inferior parietal lobule (BA 39), postcentral gyrus (BA 3, 5) and precuneus (BA 31, 7). Occipital activation included the left lingual gyrus (BA 19) and bilateral cuneus (BA 19). Other areas, such as bilateral posterior cingulate, were also associated with reading personal names (see Figure 24 and Table 6 for more details).
Reading geographical names relative to common nouns caused significant stimulation in frontal and parietal area. Activation in the frontal area included bilateral medial frontal gyri (BA 6), paracentral lobule (BA 5), precentral gyri (BA 6, 4) and superior frontal gyri (BA 9, 6). Activation in the middle frontal gyrus was only found in the right hemisphere (BA 8) (see Figure 25 and Table 7 for more details).
Characteristics of common nouns
Reading common nouns, in comparison with personal names, stimulated significantly the parieto-temporal area and the area near anterior temporal sulcus, which includes bilateral superior temporal gyri (BA 22, 38), inferior parietal lobules (BA 40), postcentral gyri (BA 1, 2), right transverse temporal gyrus (BA 42), right middle temporal gyrus (BA 21) and left supramarginal gyrus (BA 40). Frontal activation occurred dominantly in the
right hemisphere: inferior frontal gyrus (BA 47, 44) and middle frontal gyrus (BA 10).
The only left frontal activation occurred in precentral gyrus (BA 6). Other areas included left insula, bilateral cingulated gyri (BA 32) and left anterior cingulate (BA 32) (see Figure 26 and Table 8 for more details).
Reading common nouns relative to geographical names evoked activation in the bilateral ventral medial frontal area and the superior frontal gyrus (BA 10). The posterior part of temporal lobe was also activated, whereas the activation in the left hemisphere was more extended than the right side (see Figure27 and Table 9 for more details).
Stimuli Rating
The results indicate no significant difference between all word groups with regards to affective association and personal relevance {X2r (2) = 2.00, p = 0.368}. Concerning the imageability of word groups, there was a significant difference in rating {X2r (2) = 18.474, p < 0.001}. Common nouns appeared to produce more mental images than personal names {Z = -2.986, p < 0.01} and geographical names {Z = -2.829, p < 0.01}.
Personal names evoked the lowest imageability which was even significant smaller than geographical names {Z = -1.997, p < 0.05}.
L R Figure 24: Activation map (4mm slices, t-value in color bar) for visual personal names vs.
common nouns. The activation is mainly located in the frontal area.
Table 6: Regions of significant activation for comprehension of written personal names vs.
common nouns.
Region Side X Y Z T Frontal Lobe Inferior Frontal Gyrus L -44 26 15 4.73
Middle Frontal Gyrus L -42 17 25 4.85
R 26 25 43 3.13
Paracentral Lobule R 18 -40 57 3.44 Precentral Gyrus R 18 -26 60 3.30
Superior Frontal Gyrus L -18 49 38 5.26
R 20 43 37 5.07
R 22 33 44 3.97
Temporal Lobe Middle Temporal Gyrus R 42 -83 19 3.90 Superior Temporal Gyrus R 59 -59 16 5.14
Parietal Lobe Inferior Parietal Lobule R 38 -60 40 4.84 Postcentral Gyrus R 10 -34 66 3.70
R 12 -45 63 3.37
Precuneus R 10 -69 22 5.05
R 20 -70 40 4.80
Occipital Lobe Lingual Gyrus L -14 -49 -1 4.25
Cuneus L -2 -64 31 8.46
R 28 -88 25 3.97
Other areas Posterior Cingulate L -6 -51 25 6.41
R 8 -59 16 5.80
Significant at p < 0.001, uncorrected.
Table 7: Regions of significant activation for comprehension of written geographical names vs. common nouns.
Region Side X Y Z T Frontal Lobe Medial Frontal Gyrus L -2 -11 59 4.23
R 6 -9 61 3.99
Middle Frontal Gyrus R 28 27 45 5.18 Precentral Gyrus L -26 -14 60 4.01
L -16 -32 62 4.04
R 30 -22 56 3.39
Superior Frontal Gyrus R 22 17 60 3.23
L -22 48 34 4.55
Parietal Lobe Inferior Parietal Lobule R 40 -66 40 4.77
Paracentral Lobule L -4 -38 63 4.19 Postcentral Gyrus R 32 -32 61 4.02
L -32 -34 57 3.76
Precuneus L -6 -72 40 4.83
R 8 -50 54 4.23
Other areas Cingulate Gyrus L -4 -33 37 3.60 Posterior Cingulate L -4 -56 12 4.21 Significant at p < 0.001, uncorrected.
L R Figure 25: Activation map (4mm slices, t-value in color bar) for visual geographical names vs.
common nouns. Significant activation is shown in the frontal and parietal area.
L R Figure 26: Activation map (4mm slices, t-value in color bar) for visual common nouns vs.
personal names. Significant activation is shown in the right temporo-parietal junction and the left posterior temporal cortex.
Table 8: Regions of significant activation for comprehension of written common nouns vs.
personal names.
Region Side X Y Z T Frontal Lobe Inferior Frontal Gyrus R 50 17 -6 6.33
Middle Frontal Gyrus R 42 50 -4 7.51 Precentral Gyrus L -55 4 9 4.25
Temporal Lobe Transverse Temporal Gyrus R 59 -17 14 5.99 Superior Temporal Gyrus R 57 5 -7 5.39
L -59 -31 7 4.27
L -51 12 -1 4.95
Middle Temporal Gyrus R 65 -39 2 4.93
L -55 -63 12 4.83
Parietal Lobe Inferior Parietal Lobule L -61 -26 31 7.01
R 59 -33 29 6.22
L -55 -22 18 6.66
R 63 -27 40 5.61
Supramarginal Gyrus L -57 -49 36 4.76
Other areas Extra-Nuclear R 38 9 -7 5.88
Insula L -40 6 0 3.72
Cingulate Gyrus R 6 15 31 3.94
R 4 4 31 3.81
L -4 21 27 3.55
Anterior Cingulate L -6 28 21 3.20 Significant at p < 0.001, uncorrected.
Table 9: Regions of significant activation for comprehension of written common nouns vs.
geographical names.
Region Side X Y Z T Frontal Lobe Inferior Frontal Gyrus L -26 20 -25 5.66
R 48 32 -13 4.00
Medial Frontal Gyrus R 6 54 -16 5.39
R 6 56 -10 4.56
L -8 50 -11 5.38
L -8 48 -14 5.08
Middle Frontal Gyrus R 40 32 -13 4.15 Superior Frontal Gyrus R 8 56 -1 3.73
Temporal Lobe Superior Temporal Gyrus L -24 11 -22 4.65 Middle Temporal Gyrus L -59 -51 -1 4.36
R 59 -58 1 3.79
Inferior Temporal Gyrus L -57 -60 -4 3.49
Occipital Lobe Lingual Gyrus L -26 -68 -8 3.87
Parietal Lobe Inferior Parietal Lobule L -55 -34 27 3.51
Other area Anterior Cingulate L -8 45 7 3.94
Significant at p < 0.001, uncorrected.
L R Figure 27: Activation map (4mm slices, t-value in color bar) for visual common nouns vs.
geographical names. Significant activation is shown in the left posterior temporal cortex.
7.3 Discussion