Abstract

The patterns of cortical activation evoked by tactile and mechanical painful stimulation in six normal subjects and three patients with complete resection of the corpus callosum are described and compared, with emphasis on the parietal operculum. Stimulus-related cortical activation was investigated by functional magnetic resonance imaging. In both groups, painful stimulation activated the first somatosensory, insular and cingulate cortices in the contralateral hemisphere, and the parietal opercular cortex in both hemispheres. Comparison between the two patterns of cortical activation demonstrated that ipsilateral activation by unilateral painful stimulation is at least partially independent of the corpus callosum and suggests a different organization of the pain and touch systems.

Introduction

The activation of the human cerebral cortex evoked by painful stimulation has been investigated with positron emission tomog-raphy (PET), magnetoencephalography (MEG), laser evoked potentials (LEPs) and, recently, functional magnetic resonance imaging (fMRI). Whereas in all studies unilateral painful stimulation produced the activation of a region in the parietal operculum (PO), likely the second somatic sensory cortex (SII), the activation of the first somatic sensory (SI) and cingulate (Cin) cortices and of the insula (In) was inconsistent (Casey et al., 1994; Kitamura et al., 1995; Xu et al., 1997; Disbrow et al., 1998; Gelnar et al., 1999) [for a review see (Treede et al., 1999)], probably because of differences in the type of stimulation applied and the investigation techniques used (Talbot et al., 1991; Coghill et al., 1994; Derbyshire et al., 1997; Davis et al., 1998; Lenz et al., 1998; Watanabe et al., 1998; Frot et al., 1999). Activation of PO has been described in both hemispheres in most of the studies; in particular, area SII has been seen to be activated in parallel with SI (Svensson et al., 1997; Ploner et al., 1999), as well as in the absence of SI recruitment (Lenz et al., 1998; Watanabe et al., 1998; Frot et al., 1999). Indeed, the nearly identical latencies of activation of contralateral SI and SII (Kanda et al., 2000; Ploner et al., 2000) and of contralateral and ipsilateral SII (Frot and Mauguière, 1999a; Ploner et al., 1999; Kanda et al., 2000) suggest a major role for SII in pain processing (Treede et al., 2000). The altered pain sensitivity reported in patients with lesions involving PO (Greenspan and Winfield, 1992; Potagas et al., 1997; Greenspan et al., 1999) is in line with these data.

In the present work the pattern of cortical activation evoked by mechanical painful stimulation of one hand was investigated with fMRI in a group of normal volunteers and on three patients with complete surgical resection of the corpus callosum per-formed to solve medically intractable epilepsy, to establish: (i) whether activation of PO cortex by unilateral noxious stimuli was present in both hemispheres and (ii) whether ipsilateral pain-related activation of PO might be mediated by the corpus callosum. These data were compared with the activation patterns evoked by tactile stimulation.

These results have been presented in abstract form (Fabri et al., 1999b).

Materials and Methods

Six healthy volunteers (aged 34–44 years; three males, three females) and three callosotomized patients (aged 21–38 years; two males, one female) gave their informed consent to participate in the study according to the Declaration of Helsinki. The experimental protocol was approved by the Ethical Committee of the University of Ancona. The three patients had undergone complete surgical resection of the corpus callosum to reduce the spread of epileptic seizures (Fig. 1). Two of these patients (DDV, RN) had participated in a previous study (Fabri et al., 1999a). The clinical history and extent of callosal resection of all patients have been reported previously (Papo et al., 1989; Quattrini et al., 1989, 1994; Fabri et al., 1999a). All subjects were right-handed as determined by the Edinburgh handedness inventory (Oldfield, 1971). The post-operative full-scale intelligence scores (IQ performance) of patients to the Wechsler Adult Intelligence Scale (WAIS) ranged from 81 to 93.

Imaging Protocols

Subjects were placed in a 1.0 T scanner (Signa Horizon, General Electric Medical System, Milwaukee, WI) equipped with 23 mT/m gradients with their head restrained within a standard polarized head coil. They were instructed to keep their eyes closed, find a comfortable position and relax, avoiding even minimal movement; their ears were plugged. Func-tional MR images were acquired in axial or coronal planes with a single-shot T2*-weighted gradient-echo EPI sequence (TR 3000 ms, TE 60 ms, flip angle 90°, field of view 28 × 21 cm, matrix 96 × 64, 1 Nex, scan time 2.5 min). Coronal planes were orthogonal to the sagittal plane and parallel to the floor of the IVth ventricle. Axial planes were orthogonal to both the sagittal and the coronal planes. Ten contiguous 7 mm-thick axial (Fig. 2A) or coronal (Fig. 2B) sections were selected from a brain region containing the postcentral gyrus (PCG) and PO (see Fig. 2); from each selected section, 50 axial or coronal functional images were acquired during a 2.5 min stimulation cycle (one image/3 s). Overall, 500 axial or coronal functional images were thus obtained. Then high-resolution anatomical images [spoiled gradient-recalled (SPGR), 2D, TR 100 ms, TE 12 ms, flip angle 70°, field of view 28 × 21 cm, thickness 7 mm, matrix 256 × 256, 1 Nex, scan time 3 min 17 s for 10 images] were acquired in the same axial or coronal planes so that the functional images could be super-imposed on the anatomical images; the latter also allows visualization of blood vessels, which are possible sources of BOLD signals. In most subjects, four scanning sequences were acquired (tactile and painful stimulation of both hands, in the axial or the coronal plane; Table 1).

Stimulation Paradigm

Tactile stimulation consisted of brushing the subject's palm and fingers in proximo-distal direction with a rough sponge at a frequency of ~1 Hz. In all patients and in three of the six controls, stimulation was applied first to the right and then to the left hand during different scans; in the remaining three controls stimulation was applied only to the right hand (see Table 1). The stimulation session lasted 2.5 min and consisted of two 30 s stimulation periods preceded, divided and followed by a 30 s rest periods.

Painful stimulation was obtained by displacing the palm skin with a sharp wooden probe (tip diameter 0.4–0.5 mm), at 1 s intervals, to evoke pinprick pain. This kind of stimulation has been shown to be effective in activating both high-threshold mechanoreceptors with myelinated fibres (Aδ) and polymodal nociceptors with unmyelinated fibres (C) (Burgess and Perl, 1967; Perl, 1968; Bessou and Perl, 1969; Kumazawa and Perl, 1977; Torebjörk, 1974; Perl, 1984). In two of the three patients and in four of the six controls, stimulation was applied first to the right and then to the left hand during different scans; in the remaining patient and the two controls only the right hand was stimulated (see Table 1). This paradigm consisted of two 30 s stimulation periods preceded, divided and followed by a 30 s rest periods.

At the end of the stimulation session, all subjects were asked to describe their own perception of the painful stimulus by choosing among one of these definitions: not painful; not painful but annoying; painful but tolerable; and intolerably painful. All subjects reported that the stimulus was ‘painful but tolerable’. Since the perceptual threshold of pain and sharpness has been shown to be much higher than that of both Aδ and C nociceptors (Adriaensen et al., 1983; Greenspan and McGillis, 1991), normal pain perception requires considerably more than threshold activation of nociceptors; the patients' mention of a painful sensation is thus likely to indicate suprathreshold activation of nociceptors.

As control for the stimulus-related changes of signal intensity (Yetkin et al., 1996), the experimenter made the same movement 10–15 cm above the subject's hand also during the rest periods of both paradigms; in this way, any differences between the rest and the stimulation signal could be ascribed only to the administration of the stimulus.

Data Analysis

At the end of the experimental session, the images acquired were transferred to a Unix workstation (General Electric Advantage Windows 1.2) and analysed by means of custom-designed General Electric software (Functool). The software calculates a correlation coefficient that relates the time-course data to a reference function, which is a periodic square wave (Xiong et al., 1996). The first two images from each section levels (corresponding to 6 s) were not included in the analysis with a view to eliminating the transient scanner behaviour and performing the calculation on a steady state. The correlation coefficient is related to the t-parameter of Student's t-test by a precise relationship and thresholded by a confidence level selected by the operator; its value was usually 0.00001 or 0.0001, entailing a probability of 0.001 or 0.01% that the signal increase is unrelated to the reference function. For each section level, a parametric map was obtained by superimposing the 50 functional images acquired during the stimulation cycle and the anatomical image from the same section level. With the aid of a colour scale, the map displayed the degree of correlation of each pixel value with the square wave (red pixels indicate strong correlation, blue pixels poor correlation). For each activated zone, defined as a group of at least two adjacent red pixels, a ‘region of interest’ (ROI) was selected and for each ROI the software displayed the signal variation that occurred during the stimulation cycle. The area of the ROI was kept as uniform as possible among subjects and cortical areas. The signal change was then displayed as a graph where the X-axis is a temporal scale reporting the progressive number of the functional images acquired (one image/3 s) and the Y-axis represents the signal change expressed as a percentage of the signal obtained from the brain during the acquisition of the first image (baseline or 0%) of the first rest period (see Fig. 3E,F). When the signal increase, observed in ROIs selected from activated areas within regions anatomically corresponding to SI, posterior parietal (PP) cortex (in the PCG), SII (in PO, in the upper bank of the sylvian sulcus, SS), insula and Cin, was temporally correlated with the stimulus pattern, the activation in these areas was attributed to tactile or painful stimulation of the hand. Signal increases not showing temporal correlation with the stimulus pattern were considered false positives. The signal increase ranged from 2 to 5% above the baseline, depending on the cortical area studied.

The identification of the somatic sensory areas was performed by analysing their anatomical localization as defined both by standard anatomical landmarks (e.g. the ‘omega’-shaped central sulcus in the axial views) and by a reference atlas (Mai et al., 1997). To identify the position of activation foci, individual MRI scans were adjusted to the Talairach coordinate system (Talairach and Tournoux, 1988).

Further details on image acquisition, tactile stimulation paradigm and data analysis have been published elsewhere (Fabri et al., 1999a; Polonara et al., 1999).

Results

Control Subjects

In line with previous reports (Fabri et al., 1999a; Polonara et al., 1999), cortical activation to tactile stimulation of one hand was consistently observed in SI in the anterior parietal (AP) cortex of the contralateral hemisphere and in PO (Fig. 3A) and the PP cortices of both hemispheres (Table 2). The mean Talairach stereotaxic coordinates of touch-related activation foci in contralateral and ipsilateral PO (Table 3) corresponded to the accepted localization of area SII in man (Burton et al., 1997; Frot and Mauguière, 1999b; Disbrow et al, 2000). Activation foci were also detected in other cortical regions of the contralateral hemisphere: Cin in three cases, the precentral gyrus and In in two cases (Table 2).

Painful mechanical stimulation of one hand evoked cortical activation in contralateral AP, PP and PO in all six subjects (Fig. 3B); in five cases the Cin cortex was also activated, and in four subjects the insular cortex. In the ipsilateral hemisphere, activation of PP and PO (Fig. 3B) was consistently present, the In cortex was activated in two subjects and Cin in two (Table 2). The mean Talairach stereotaxic coordinates of pain-related activation foci in bilateral PO (see Table 3) were similar to data reported in previous pain studies (Frot et al., 1999; Ploner et al., 1999).

Callosotomized Patients

The three patients (DDC, DDV, RN) had undergone the complete resection of the corpus callosum (Fig. 1) and were studied 36–123 months from callosotomy.

As in control subjects, the contralateral pattern of cortical activation to unilateral tactile stimulation of the hand included activation foci in SI, PO (Fig. 3C) and PP (Table 4) as well as in Cin (one case; Table 4) and the precentral gyrus. At variance with normal subjects, no cortical activation was evoked by tactile stimulation of one hand in the ipsilateral hemisphere (Table 4; Fig. 3C). Similar results were obtained from all patients. Figure 3C and E show data from patient DDV. Tactile stimulation of the right hand activated a region in the contralateral PO (Fig. 3C) in which the signal increased by ~2% above the baseline during the stimulation periods (Fig. 3E). The mean Talairach stereotaxic coordinates of touch-related activation foci in contra-lateral PO were x = 50, y = –27 and z = 19 (Table 5). No activated zones were observed in the ipsilateral PO. These results are in agreement with previous descriptions (Fabri et al., 1999a, Fabri et al2001).

As regards painful stimulation, contralateral activation was observed in PO in all patients (Fig. 3D), in AP in two cases (DDC, RN) and in PP in one case (DDV); the insular cortex was activated in one case (DDC; Table 3). In the ipsilateral hemisphere, PO was also activated in all patients (Fig. 3D; Table 3), the insular cortex was activated in one case (DDC) and PP in another (DDV), whereas AP and Cin were never activated. Similar results were obtained from all patients. Figure 3D and F shows data from patient DDV. Painful stimulation of the right hand evoked activation in the PO of both hemispheres (Fig. 3D). The signal increase was ~3% in the contralateral and 2% in the ipsilateral PO during the two stimulation periods (Fig. 3F). The mean Talairach stereotaxic coordinates of pain-related activation foci in contralateral PO were x = 53, y = –17 and z = 17, and in ipsilateral PO x = –49, y = – 20 and z = 17 (Table 5).

The analysis of these data indicates that painful stimulation of either hand activated similar regions of PO in both hemispheres and generally evoked activation foci in PO regions more anterior and/or more medial than those activated by tactile stimulation (compare, for example, touch-evoked focus 1 in Fig. 3A and pain-evoked focus 1 in Fig. 3B). In addition, painful stimulation often evoked multiple activation foci in PO in each hemisphere; in these cases, at least one of them overlapped with that evoked by tactile stimulation (Fig. 3) (Davis et al., 1998).

Discussion

The main finding of this study was that unilateral painful stimulation of the hand bilaterally activated PO, in both control subjects and in patients with complete resection of the corpus callosum.

The noxious stimulus used in this study consisted of pricking the palm with a sharp wooden probe, a type of mechanical stimulation that has been shown to activate both Aδ and C nociceptors (Burgess and Perl, 1967; Perl, 1968; Bessou and Perl, 1969; Torebjörk, 1974; Kumazawa and Perl, 1977; Perl, 1984). The painful sensation, slight but distinctly felt by all subjects, indicates that both Aδ and C nociceptors were activated by this kind of stimulus (Adriaensen et al., 1983; Greenspan and McGillis, 1991).

In two previous papers we reported that patients with com-plete or partial callosotomy involving the fibres running in the posterior third of the body of the callosal commissure failed to exhibit activation of ipsilateral PO after tactile stimulation of one hand (Fabri et al., 1999a, Fabri et al2001). In the present study, two of those same subjects and a third patient also subjected to complete callosal resection, showed activation of ipsilateral PO after unilateral painful stimulation, suggesting that this activa-tion was selectively evoked by the noxious stimulus.

A psychophysical study of a totally callosotomized patient (Stein et al., 1989) has shown that each hemisphere may be aware of the ipsilateral noxious stimulus, provided it is very intense, suggesting that at least some aspects of pain percep-tion from the ipsilateral body surface do not require the interhemispheric transfer of information. The possibility of the extracallosal activation of ipsilateral PO has been suggested by several investigators: for instance, the simultaneous activation of ipsilateral and contralateral PO recorded in latency studies in normal subjects (Kagiki et al., 1995; Kitamura et al., 1995, 1997; Ploner et al., 1999; Kanda et al., 2000) has been explained with uncrossed subcortical pathways. However, successive activation of contralateral PO and ipsilateral PO with a delay compatible with callosal transmission time has also been observed (Frot et al., 1999).

By showing that unilateral painful stimulation of the hand evokes bilateral activation of PO in totally callosotomized patients, the present study: (i) confirms previous results that PO is bilaterally involved in pain processing and (ii) demonstrates that activation of ipsilateral PO is at least partially independent of callosal transmission, being probably mediated by extracallosal pathways: uncrossed subcortical pathways (Frot and Mauguière, 1999a), subcortical commissures, or both.

In conclusion, two somatosensory modalities, touch and nociception, appear to activate PO bilaterally in different ways: both tactile and pain afferents reach the contralateral PO via the lateral lemniscal system, and the ipsilateral PO through the contralateral hemisphere and corpus callosum (Fabri et al., 1999a); painful afferences also gain access to the ipsilateral PO via extracallosal pathways. Consequently, bilateral activation of PO may occur simultaneously. This finding supports the hypothesis of a major role for PO in pain processing (Treede et al., 2000). It thus seems likely that the pain system has a simpler organization than the tactile system (Ploner et al., 1999, 2000). This may mean that pain perception requires reaction to, and avoidance of, harmful stimuli rather than sophisticated sensory capacities.

Notes

The authors are grateful to Professors Salvatore Aglioti, Fiorenzo Conti, Tullio Manzoni and Giancarlo Tassinari and to Dr Andrea Minelli for helpful criticisms, and to Ms Silvia Modena for editing the English. Supported by MURST (Ministero Università e Ricerca Scientifica e Tecnologica, 1999, 2001) and CNR (Consiglio Nazionale delle Ricerche, 99.02520.CT04).

Table 1

Summary of the experimental cases

Subject Age (years) Sex Callosal resection Right-hand stimulation Left-hand stimulation Axial images Coronal images 
T = tactile stimulation; P = painful stimulation. 
aExamined twice. 
Controls        
    MFa 41 no T + P yes yes 
    AP 44 no T + P T + P no yes 
    EP 35 no T + P T + P yes no 
    GP 34 no T + P no no yes 
    RPa 41 no T + P no no yes 
    FT 34 no T + P T + P no yes 
Patients        
    DDC 21 yes T + P no yes 
    DDV 35 yes T + P T + P yes no 
    RN 38 yes T + P T + P yes no 
Subject Age (years) Sex Callosal resection Right-hand stimulation Left-hand stimulation Axial images Coronal images 
T = tactile stimulation; P = painful stimulation. 
aExamined twice. 
Controls        
    MFa 41 no T + P yes yes 
    AP 44 no T + P T + P no yes 
    EP 35 no T + P T + P yes no 
    GP 34 no T + P no no yes 
    RPa 41 no T + P no no yes 
    FT 34 no T + P T + P no yes 
Patients        
    DDC 21 yes T + P no yes 
    DDV 35 yes T + P T + P yes no 
    RN 38 yes T + P T + P yes no 
Table 2

Cortical areas activated by tactile (T) and painful (P) stimulation in control subjects

Subject Contralateral hemisphere Ipsilateral hemisphere 
 SI PP SII In Cin SI PP SII In Cin 
 
The + symbol indicates the presence of activation temporally correlated with the stimulus pattern. The – symbol indicated absence of activation temporally correlated with the stimulus pattern. 
MF – – – – – – 
AP – – – – – – 
EP – – – – – – – – 
GP – – – – – – – – – 
RP – – – – – – – 
FT – – – – – – 
Subject Contralateral hemisphere Ipsilateral hemisphere 
 SI PP SII In Cin SI PP SII In Cin 
 
The + symbol indicates the presence of activation temporally correlated with the stimulus pattern. The – symbol indicated absence of activation temporally correlated with the stimulus pattern. 
MF – – – – – – 
AP – – – – – – 
EP – – – – – – – – 
GP – – – – – – – – – 
RP – – – – – – – 
FT – – – – – – 
Table 3

Talairach and Tournoux coordinates of the activated zones in PO of control subjects

 Tactile stimulation Painful stimulation 
 PO contra PO ipsi  PO contra PO ipsi 
 x y z x y z x y z x y z 
x, lateral–medial axis; y, anterior–posterior axis; z, vertical axis (Talairach and Tournoux, 1988). 
MF 48 –15 16 –58 –20 16 35 –27 16 –45 –28 16 
AP 50 –24 23 –38 –24 22 48 –20 22 –35 –20 19 
EP 56 –18 16 –52 –16 16 48 –12 16 –58 –16 16 
GP 58 –30 23 –58 –30 32 58 –24 27 –58 –24 32 
RP 43 –24 25 –51 –24 20 56 –20 21 –60 –20 15 
FT 57 –20 18 –53 –20 19 62 –20 15 –54 –20 20 
 
Mean 52 –22 20 –52 –22 21 51 –21 20 –52 –21 20 
SD  5.3  7.3  4.8  5.9  9.7  4.7  9.8  4.1  6.3 
 Tactile stimulation Painful stimulation 
 PO contra PO ipsi  PO contra PO ipsi 
 x y z x y z x y z x y z 
x, lateral–medial axis; y, anterior–posterior axis; z, vertical axis (Talairach and Tournoux, 1988). 
MF 48 –15 16 –58 –20 16 35 –27 16 –45 –28 16 
AP 50 –24 23 –38 –24 22 48 –20 22 –35 –20 19 
EP 56 –18 16 –52 –16 16 48 –12 16 –58 –16 16 
GP 58 –30 23 –58 –30 32 58 –24 27 –58 –24 32 
RP 43 –24 25 –51 –24 20 56 –20 21 –60 –20 15 
FT 57 –20 18 –53 –20 19 62 –20 15 –54 –20 20 
 
Mean 52 –22 20 –52 –22 21 51 –21 20 –52 –21 20 
SD  5.3  7.3  4.8  5.9  9.7  4.7  9.8  4.1  6.3 
Table 4

Cortical areas activated by tactile (T) and painful (P) stimulation in callosotomized patients

Subject Contralateral hemisphere Ipsilateral hemisphere 
 SI PP SII In Cin SI PP SII In Cin 
 
The + symbol indicates the presence of activation temporally correlated with the stimulus pattern. The – symbol indicated absence of activation temporally correlated with the stimulus pattern. 
DDC – – – – – – – – – – – – 
DDV – – – – – – – – – – – – 
RN – – – – – – – – – – – – – – 
Subject Contralateral hemisphere Ipsilateral hemisphere 
 SI PP SII In Cin SI PP SII In Cin 
 
The + symbol indicates the presence of activation temporally correlated with the stimulus pattern. The – symbol indicated absence of activation temporally correlated with the stimulus pattern. 
DDC – – – – – – – – – – – – 
DDV – – – – – – – – – – – – 
RN – – – – – – – – – – – – – – 
Table 5

Talairach and Tournoux coordinates of the activated zones in PO of callosotomized patients

 Tactile stimulation Painful stimulation 
 PO contra PO contra PO ipsi 
 x y z x y z x y z 
x, lateral–medial axis; y, anterior–posterior axis; z, vertical axis (Talairach and Tournoux, 1988). 
DDC 54 –32 25 57 –20 20 –58 –20 20 
DDV 43 –25 16 48 –18 16 –46 –14 16 
RN 52 –23 16 53 –12 16 –42 –25 16 
 
Mean 50 –27 19  53 –17 17 –49 –20 17 
SD 5.9  4.7  5.2  4.5  4.2  2.3  8.3  5.5  2.3 
 Tactile stimulation Painful stimulation 
 PO contra PO contra PO ipsi 
 x y z x y z x y z 
x, lateral–medial axis; y, anterior–posterior axis; z, vertical axis (Talairach and Tournoux, 1988). 
DDC 54 –32 25 57 –20 20 –58 –20 20 
DDV 43 –25 16 48 –18 16 –46 –14 16 
RN 52 –23 16 53 –12 16 –42 –25 16 
 
Mean 50 –27 19  53 –17 17 –49 –20 17 
SD 5.9  4.7  5.2  4.5  4.2  2.3  8.3  5.5  2.3 
Figure 1.

MR images of midsagittal brain slices obtained from T1-weighted spin-echo sequences showing the extent of callosal resection in the three patients (DDC, DDV, RN).

Figure 1.

MR images of midsagittal brain slices obtained from T1-weighted spin-echo sequences showing the extent of callosal resection in the three patients (DDC, DDV, RN).

Figure 2.

Schematic drawing of the lateral view of the human brain, showing the axial (A) and coronal (B) planes from which the images were acquired. Anterior is on the left. CS, central sulcus; SS, sylvian sulcus; PCG is posterior to CS; PO is in the depth of SS.

Figure 2.

Schematic drawing of the lateral view of the human brain, showing the axial (A) and coronal (B) planes from which the images were acquired. Anterior is on the left. CS, central sulcus; SS, sylvian sulcus; PCG is posterior to CS; PO is in the depth of SS.

Figure 3.

Cortical activation during tactile and painful stimulation of the right hand in a representative subject from the control group (EP; A,B) and in a patient with total resection of the corpus callosum (DDV; CF), representative of the patient group. Left hemisphere on the right. (A) Axial image obtained from an SPGR T1-weighted sequence on which the cortical areas activated in the parietal operculum (PO) by tactile stimulation of the right hand (obtained from a single-shot EPI sequence) have been superimposed. Numbers 1 and 3 indicate the contralateral and ipsilateral activation foci, respectively. (B) Axial image obtained as in (A), showing the cortical areas activated in the parietal operculum by painful stimulation of the right hand. 1, 2, Contralateral foci; 3, 4, ipsilateral foci. (C) Axial image obtained as in (A), showing the activation in the contralateral PO (foci 1 and 2) due tactile stimulation of the right hand. No activation was detected in the ipsilateral PO in this and adjacent sections. (D) Axial image showing the activation of PO by painful stimulation of the right hand. Activation is present both in contralateral (1 and 2) and ipsilateral (3) PO. (E) graph illustrating the signal increase in ROI 1, shown in (C) in contralateral PO. The two red continuous lines on the X-scale (from images 8–18 and from 28 to 38) mark the two 30 s stimulation periods. The signal intensity change is expressed as the percentage of the signal obtained at rest (0% level). (F) Graphs showing the signal variation in the corresponding ROIs selected in the contralateral (ROI 2) and ipsilateral (ROI 3) PO shown in (D). SS, sylvian sulcus.

Figure 3.

Cortical activation during tactile and painful stimulation of the right hand in a representative subject from the control group (EP; A,B) and in a patient with total resection of the corpus callosum (DDV; CF), representative of the patient group. Left hemisphere on the right. (A) Axial image obtained from an SPGR T1-weighted sequence on which the cortical areas activated in the parietal operculum (PO) by tactile stimulation of the right hand (obtained from a single-shot EPI sequence) have been superimposed. Numbers 1 and 3 indicate the contralateral and ipsilateral activation foci, respectively. (B) Axial image obtained as in (A), showing the cortical areas activated in the parietal operculum by painful stimulation of the right hand. 1, 2, Contralateral foci; 3, 4, ipsilateral foci. (C) Axial image obtained as in (A), showing the activation in the contralateral PO (foci 1 and 2) due tactile stimulation of the right hand. No activation was detected in the ipsilateral PO in this and adjacent sections. (D) Axial image showing the activation of PO by painful stimulation of the right hand. Activation is present both in contralateral (1 and 2) and ipsilateral (3) PO. (E) graph illustrating the signal increase in ROI 1, shown in (C) in contralateral PO. The two red continuous lines on the X-scale (from images 8–18 and from 28 to 38) mark the two 30 s stimulation periods. The signal intensity change is expressed as the percentage of the signal obtained at rest (0% level). (F) Graphs showing the signal variation in the corresponding ROIs selected in the contralateral (ROI 2) and ipsilateral (ROI 3) PO shown in (D). SS, sylvian sulcus.

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