**2.1 Dual-task effect on belief-bias reasoning**

Tsujii & Watanabe (2009) examined the relationship between dual-task effect and IFC activity during belief-bias reasoning by fNIRS. Previous behavioural studies demonstrated that subjects with poor working memory capacity exhibited larger belief-bias effect than those with rich working memory capacity (De Neys, 2006a, 2006b; Stanovich & West, 2000). More directly, De Neys (2006a) found that attention-demanding concurrent tasks impaired incongruent but not congruent reasoning trials. These findings suggest that the analytic system is attention-demanding, and that when attention is divided by a concurrent task, individuals tend to rely on the automatic heuristic system, resulting in belief-bias responses. Although these behavioural findings are important, the neural correlates of dual-task reasoning are still unclear.

Tsujii & Watanabe (2009) therefore examined the neural correlates of the dual-task effect on IFC activity in belief-bias reasoning using fNIRS approach. Subjects were asked to perform a syllogistic reasoning task, involving congruent and incongruent trials, while responding to attention-demanding secondary tasks, in which a white square stimulus appeared at one of the four corners of a black screen throughout the experiment (Fig. 3). In the low-load condition, subjects were required to respond whenever the stimulus was in a predetermined location (e.g. upper-left position). In the high-load condition, subjects were asked to respond when the current stimulus was in the same location as the stimulus two trials previously (2-back).

Fig. 3. Time schedule and schematic drawings of the secondary task.

Behavioural analysis showed that the high-load secondary task impaired only incongruent reasoning performance. NIRS analysis found that the high-load secondary task decreased right IFC activity during incongruent trials. Correlation analysis showed that subjects with enhanced right IFC activity could perform better in the incongruent reasoning trials, though subjects for whom right IFC activity was impaired by the secondary task could not maintain better reasoning performance. These findings suggest that the right IFC may be responsible for the dual-task effect in conflicting reasoning processes. When secondary tasks impair right IFC activity, subjects may rely on the automatic heuristic system, which results in belief-bias responses. Tsujii & Watanabe (2009) therefore offer the first demonstration of neural correlates of dual-task effect on IFC activity in belief-bias reasoning.

#### **2.2 Belief-bias reasoning under time-pressure**

38 Advances in Brain Imaging

and heavily demanding of computational resources. Although these claims were supported by behavioural findings (De Neys, 2006a, 2006b), the neural correlates of dual-task and timepressure effect on belief-bias reasoning was unknown. Thus, a series of fNIRS studies in our laboratory examined the attention-demanding and time-consuming properties of the analytic reasoning system and IFC activity using fNIRS (Tsujii & Watanabe, 2009, 2010). In addition, we examined the aging effect on hemispheric asymmetry in IFC activity using

Tsujii & Watanabe (2009) examined the relationship between dual-task effect and IFC activity during belief-bias reasoning by fNIRS. Previous behavioural studies demonstrated that subjects with poor working memory capacity exhibited larger belief-bias effect than those with rich working memory capacity (De Neys, 2006a, 2006b; Stanovich & West, 2000). More directly, De Neys (2006a) found that attention-demanding concurrent tasks impaired incongruent but not congruent reasoning trials. These findings suggest that the analytic system is attention-demanding, and that when attention is divided by a concurrent task, individuals tend to rely on the automatic heuristic system, resulting in belief-bias responses. Although these behavioural findings are important, the neural correlates of dual-task

Tsujii & Watanabe (2009) therefore examined the neural correlates of the dual-task effect on IFC activity in belief-bias reasoning using fNIRS approach. Subjects were asked to perform a syllogistic reasoning task, involving congruent and incongruent trials, while responding to attention-demanding secondary tasks, in which a white square stimulus appeared at one of the four corners of a black screen throughout the experiment (Fig. 3). In the low-load condition, subjects were required to respond whenever the stimulus was in a predetermined location (e.g. upper-left position). In the high-load condition, subjects were asked to respond when the current stimulus was in the same location as the stimulus two trials previously (2-back).

Fig. 3. Time schedule and schematic drawings of the secondary task.

fNIRS (Tsujii et al., 2010b).

reasoning are still unclear.

**2.1 Dual-task effect on belief-bias reasoning** 

Tsujii & Watanabe (2010) addressed the difference in speed between the heuristic and analytic reasoning systems. The dual-process theory of reasoning explained the belief-bias effect by proposing a belief-based fast heuristic system and a logic-based slow analytic system. Although the claims were supported by behavioural findings that the belief-bias effect was enhanced when subjects were not given sufficient time for reasoning (De Neys, 2006b; Evans & Curtis-Holmes, 2005), the neural correlates were still unknown. Tsujii & Watanabe (2010), thus, examined the neural correlates of the time-pressure effect on the IFC activity in belief-bias reasoning using fNIRS. Subjects were asked to perform a syllogistic reasoning task, involving congruent and incongruent trials, both in long-span (20 s) and short-span conditions (10 s).

Behavioural analysis found that only incongruent reasoning performance was impaired by the time-pressure of short-span trials. NIRS analysis found that the time-pressure decreased right IFC activity during incongruent trials. Correlation analysis showed that subjects with enhanced right IFC activity could perform better in incongruent trials, while subjects for whom the right IFC activity was impaired by the time-pressure could not maintain better reasoning performance. These findings suggest that the right IFC may be responsible for the time-pressure effect in conflicting reasoning processes. When the right IFC activity was impaired in the short-span trials in which subjects were not given sufficient time for reasoning, the subjects may rely on the fast heuristic system, which result in belief-bias responses. Tsujii & Watanabe (2010) therefore offer the first demonstration of neural correlates of time-pressure effect on the IFC activity in belief-bias reasoning.

#### **2.3 Aging and belief-bias reasoning**

Behavioural Tsujii et al. (2010b) examined the difference in neural activity associated with deductive reasoning processes between young and older adults. Some behavioural studies reported that older adults exhibited a larger belief-bias effect than young adults (De Neys & Van Gelder, 2009), though the neural correlates of the aging effect on belief-bias reasoning remained unknown. Therefore, Tsujii et al. (2010b) examined IFC activity differences in belief-bias reasoning between young (mean age, 21.50 years) and older subjects (mean age, 68.53 years) using fNIRS.

Behavioural analysis found that older adults exhibited a larger belief-bias than young adults. Although the belief-bias effect was significant in both age groups, the size of the

Neural Mechanisms for Dual-Process Reasoning: Evidence from the Belief-Bias Effect 41

Despite these shortcomings, use of NIRS is becoming increasingly common in recent neuroimaging studies, because of its advantages, such as exceptional safety, low cost and robustness against body movement. Indeed, recent NIRS studies have established the utility of NIRS in various cognitive tasks involving working memory (Ehlis et al., 2008; Tsujii et al. 2007, 2009b, 2010c), response inhibition (Boecker et al., 2007; Tsujii et al., 2011b), and semantic memory retrieval (Herrmann et al., 2003, 2004; Tsujii et al., 2009a). We believe that

fNIRS is also expected to facilitate the investigation of wide subject populations, including young children (Minagawa-Kawai et al., 2008; Tsujii et al., 2009b) and the elderly (Herrmann et al., 2006; Kameyama et al., 2004). Children and elderly subjects have been found to exhibit a larger belief-bias effect than young adults (De Neys and Van Gelder, 2009). It is thus important to examine the neural mechanisms in these subject populations in reasoning research. In deed, we successfully demonstrated the hemispheric difference of IFC activity between young and older adults in the belief-bias reasoning task (Tsujii et al. 2010b). We believe that fNIRS will improve understanding of the neural substrates of reasoning

Although neuroimaging studies, such as fMRI and fNIRS, have provided useful insights of the neural mechanisms of deductive reasoning, they can only examine correlations between cortical areas and a type of behaviour. In contrast, the rTMS approach can establish the causal relationships between brain and behaviour more directly compared with fMRI and fNIRS. In our laboratory, an off-line method of rTMS was adopted to examine the neural correlates of deductive reasoning. In the off-line method, low-frequency rTMS is delivered to a specific brain area over several minutes to disrupt normal functioning of this area transiently after stimulation (see Robertson et al., 2003 for detailed review). For example, Devlin et al. (2003) delivered low-frequency (1Hz) magnetic stimulation at IFC region for 10 min and found that the semantic processing was disrupted in a semantic decision task. In the first experiment, we examine the effect of low-frequency magnetic stimulation at IFC region on performance of congruent and incongruent reasoning performance (Tsujii et al., 2010a). In the second experiment (Tsujii et al., 2011a), we investigated the effect of rTMS at SPL (superior parietal lobule) on the performance of abstract reasoning in which semantic content was lacking (e.g.,

Tsujii et al. (2010a) examined the role of IFC in belief-bias reasoning using rTMS approach. Subjects participated in a belief-bias reasoning task for 10 min (pre-test), then received lowfrequency (1 Hz) rTMS in the left or right IFC for 10 min, and finally performed a reasoning task again for 10 min (post-test). The reasoning task included congruent and incongruent trials. For control conditions, we used a specially designed sham coil with the same visual appearance and same audible clicking sound as the TMS coil but without production of any magnetic field. There was no significant difference between TMS and sham condition in the pre-test. Our interest was the TMS effect on performance of congruent and incongruent

"All P is B"). The stimulation sites of IFC and SPL were presented in Fig. 4.

NIRS will improve understanding of the neural substrates of reasoning processes.

processes.

**3. TMS study in deductive reasoning** 

**3.1 The role of IFC in belief-bias reasoning** 

reasoning trials in the post-test.

effect was significantly larger for older than young adults. In the belief-bias reasoning paradigm, automatic semantic processing interferes with reasoning performance in incongruent trials. Subjects were thus required to inhibit irrelevant semantic processing to resolve the conflicting reasoning. However, it is generally known that older adults are less able to inhibit task-irrelevant information processing than young adults. This may be one of the reasons that older adults exhibited a larger belief-bias effect in deductive reasoning.

NIRS analysis showed that the right IFC was more activated than the left IFC in young adults, while there was no significant difference between the right and left IFCs in older adults. That is, hemispheric asymmetry of IFC activation (right-lateralization) was only observed in young subjects. In addition, the reduced lateralization of older adults was not due to reduction of right IFC activity, but due to enhancement of left IFC activity. These results are in line with numerous fMRI findings that showed age-related reduction of hemispheric asymmetry and over-recruitment in prefrontal activity in several tasks (Cabeza et al., 1997, 2002, 2004; Langenecker et al., 2004, 2007; Nielson et al., 2002, 2004; Rajah & McIntosh, 2008; Rympa & D'Esposito, 2000). For example, older adults often show bilateral activation in tasks associated with left-lateralized activity in young adults, such as verbal working memory and semantic processing tasks (Bergerbest et al., 2009; Rajah & McIntosh, 2008; Rympa & D'Esposito, 2000). Likewise, older adults often show bilateral activation in tasks associated with right-lateralized activity in young adults such as episodic retrieval and response inhibition tasks (Langenecker & Nielson, 2003; Nielson et al., 2002, 2004).

With regard to the function of age-related lateralization reduction, two main interpretations have been proposed: the compensatory and dedifferentiation hypotheses. The compensation hypothesis considers that older adults recruit more areas of the contralateral hemisphere than younger adults in order to achieve or attempt to achieve the same levels of performance (Reuter-Lorenz et al., 2000). In contrast, the dedifferentiation hypothesis considers that the additional recruitment reflects a generalized spreading of activity due to reduced specialization of function, regardless of whether it has a compensatory effect (Logan et al., 2002). Tsujii et al. (2010b) conducted the correlation analysis which revealed that the positive correlation between reasoning accuracy and IFC activation was significant in both hemispheres for older subjects, while a significant correlation was only found in the right hemisphere for young subjects. These findings are consistent with the compensatory hypothesis that older adults may recruit the left IFC to compensate for the age-related decline of inhibitory control functions.

#### **2.4 Utility of fNIRS in reasoning studies**

In the present chapter, we introduced fNIRS approach to elucidate the neural mechanisms of deductive reasoning processes, although most of the previous studies used fMRI technique (Goel et al., 2000; Goel and Dolan, 2001, 2003; Knauff et al., 2002, 2003; Monti et al., 2007, 2009; Stavy et al., 2006). Certain shortcomings of the NIRS technique thus need to be mentioned. First, NIRS can detect hemodynamic changes only at the surface of the brain (about 2 cm beneath the skull). Subcortical responses thus cannot be examined using NIRS. In particular, activity in the anterior cingulate cortex, which is known to be associated with conflict detection and is probably an important neural locus of belief-bias reasoning (Goel, 2007; De Neys et al., 2008), cannot be examined by NIRS. Second, NIRS features relatively low spatial resolution compared with fMRI, making precise analysis with it difficult.

Despite these shortcomings, use of NIRS is becoming increasingly common in recent neuroimaging studies, because of its advantages, such as exceptional safety, low cost and robustness against body movement. Indeed, recent NIRS studies have established the utility of NIRS in various cognitive tasks involving working memory (Ehlis et al., 2008; Tsujii et al. 2007, 2009b, 2010c), response inhibition (Boecker et al., 2007; Tsujii et al., 2011b), and semantic memory retrieval (Herrmann et al., 2003, 2004; Tsujii et al., 2009a). We believe that NIRS will improve understanding of the neural substrates of reasoning processes.

fNIRS is also expected to facilitate the investigation of wide subject populations, including young children (Minagawa-Kawai et al., 2008; Tsujii et al., 2009b) and the elderly (Herrmann et al., 2006; Kameyama et al., 2004). Children and elderly subjects have been found to exhibit a larger belief-bias effect than young adults (De Neys and Van Gelder, 2009). It is thus important to examine the neural mechanisms in these subject populations in reasoning research. In deed, we successfully demonstrated the hemispheric difference of IFC activity between young and older adults in the belief-bias reasoning task (Tsujii et al. 2010b). We believe that fNIRS will improve understanding of the neural substrates of reasoning processes.

### **3. TMS study in deductive reasoning**

40 Advances in Brain Imaging

effect was significantly larger for older than young adults. In the belief-bias reasoning paradigm, automatic semantic processing interferes with reasoning performance in incongruent trials. Subjects were thus required to inhibit irrelevant semantic processing to resolve the conflicting reasoning. However, it is generally known that older adults are less able to inhibit task-irrelevant information processing than young adults. This may be one of the reasons that older adults exhibited a larger belief-bias effect in deductive reasoning.

NIRS analysis showed that the right IFC was more activated than the left IFC in young adults, while there was no significant difference between the right and left IFCs in older adults. That is, hemispheric asymmetry of IFC activation (right-lateralization) was only observed in young subjects. In addition, the reduced lateralization of older adults was not due to reduction of right IFC activity, but due to enhancement of left IFC activity. These results are in line with numerous fMRI findings that showed age-related reduction of hemispheric asymmetry and over-recruitment in prefrontal activity in several tasks (Cabeza et al., 1997, 2002, 2004; Langenecker et al., 2004, 2007; Nielson et al., 2002, 2004; Rajah & McIntosh, 2008; Rympa & D'Esposito, 2000). For example, older adults often show bilateral activation in tasks associated with left-lateralized activity in young adults, such as verbal working memory and semantic processing tasks (Bergerbest et al., 2009; Rajah & McIntosh, 2008; Rympa & D'Esposito, 2000). Likewise, older adults often show bilateral activation in tasks associated with right-lateralized activity in young adults such as episodic retrieval and

response inhibition tasks (Langenecker & Nielson, 2003; Nielson et al., 2002, 2004).

decline of inhibitory control functions.

**2.4 Utility of fNIRS in reasoning studies** 

With regard to the function of age-related lateralization reduction, two main interpretations have been proposed: the compensatory and dedifferentiation hypotheses. The compensation hypothesis considers that older adults recruit more areas of the contralateral hemisphere than younger adults in order to achieve or attempt to achieve the same levels of performance (Reuter-Lorenz et al., 2000). In contrast, the dedifferentiation hypothesis considers that the additional recruitment reflects a generalized spreading of activity due to reduced specialization of function, regardless of whether it has a compensatory effect (Logan et al., 2002). Tsujii et al. (2010b) conducted the correlation analysis which revealed that the positive correlation between reasoning accuracy and IFC activation was significant in both hemispheres for older subjects, while a significant correlation was only found in the right hemisphere for young subjects. These findings are consistent with the compensatory hypothesis that older adults may recruit the left IFC to compensate for the age-related

In the present chapter, we introduced fNIRS approach to elucidate the neural mechanisms of deductive reasoning processes, although most of the previous studies used fMRI technique (Goel et al., 2000; Goel and Dolan, 2001, 2003; Knauff et al., 2002, 2003; Monti et al., 2007, 2009; Stavy et al., 2006). Certain shortcomings of the NIRS technique thus need to be mentioned. First, NIRS can detect hemodynamic changes only at the surface of the brain (about 2 cm beneath the skull). Subcortical responses thus cannot be examined using NIRS. In particular, activity in the anterior cingulate cortex, which is known to be associated with conflict detection and is probably an important neural locus of belief-bias reasoning (Goel, 2007; De Neys et al., 2008), cannot be examined by NIRS. Second, NIRS features relatively

low spatial resolution compared with fMRI, making precise analysis with it difficult.

Although neuroimaging studies, such as fMRI and fNIRS, have provided useful insights of the neural mechanisms of deductive reasoning, they can only examine correlations between cortical areas and a type of behaviour. In contrast, the rTMS approach can establish the causal relationships between brain and behaviour more directly compared with fMRI and fNIRS. In our laboratory, an off-line method of rTMS was adopted to examine the neural correlates of deductive reasoning. In the off-line method, low-frequency rTMS is delivered to a specific brain area over several minutes to disrupt normal functioning of this area transiently after stimulation (see Robertson et al., 2003 for detailed review). For example, Devlin et al. (2003) delivered low-frequency (1Hz) magnetic stimulation at IFC region for 10 min and found that the semantic processing was disrupted in a semantic decision task. In the first experiment, we examine the effect of low-frequency magnetic stimulation at IFC region on performance of congruent and incongruent reasoning performance (Tsujii et al., 2010a). In the second experiment (Tsujii et al., 2011a), we investigated the effect of rTMS at SPL (superior parietal lobule) on the performance of abstract reasoning in which semantic content was lacking (e.g., "All P is B"). The stimulation sites of IFC and SPL were presented in Fig. 4.

#### **3.1 The role of IFC in belief-bias reasoning**

Tsujii et al. (2010a) examined the role of IFC in belief-bias reasoning using rTMS approach. Subjects participated in a belief-bias reasoning task for 10 min (pre-test), then received lowfrequency (1 Hz) rTMS in the left or right IFC for 10 min, and finally performed a reasoning task again for 10 min (post-test). The reasoning task included congruent and incongruent trials. For control conditions, we used a specially designed sham coil with the same visual appearance and same audible clicking sound as the TMS coil but without production of any magnetic field. There was no significant difference between TMS and sham condition in the pre-test. Our interest was the TMS effect on performance of congruent and incongruent reasoning trials in the post-test.

Neural Mechanisms for Dual-Process Reasoning: Evidence from the Belief-Bias Effect 43

Tsujii et al. (2011a) examined the effect of IFC stimulation on abstract reasoning trials in which semantic content was lacking (e.g. "All P are B"), as well as content reasoning trials which involved the congruent and incongruent trials. In contrast of the incongruent reasoning performance, we did not find the significant IFC stimulation effect on abstract reasoning performance. Right IFC stimulation impaired only incongruent trials. These findings suggest that the right IFC may not the neural locus of the analytic reasoning system. Rather, the right IFC may play a role in blocking the belief-based heuristic system (left IFC) in solving incongruent reasoning trials. On the other hand, individuals need not actively inhibit the heuristic processing on abstract trials, so right IFC stimulation did not

 So, where is the neural locus responsible for abstract reasoning performance? Tsujii et al (2011a) magnetically stimulated SPL (superior parietal lobule: BA = 7). In contrast to the IFC stimulation, bilateral SPL stimulation significantly impaired abstract reasoning performance. This is consistent with previous fMRI studies which showed that the abstract reasoning performance significantly activated the SPL region (Goel et al., 2000; Goel & Dolan, 2001; Knauff et al., 2002, 2003). In general, SPL is associated with spatial processing based on evidence from fMRI (Takahama et al., 2010; Thakral & Slotnick, 2009), neurological patients (Ferber & Danckert, 2006; Shinoura et al., 2009) and TMS studies (Hamidi et al., 2008, 2009). Some authors have claimed that cognitive processes of constructing and manipulating spatially organized mental models are essential for deductive reasoning (Johnson-Laird, 1999, 2001). The mental models are a form of representation that can be spatial but more abstract. Phenomenological reports in the reasoning literature often have suggested that subjects may solve abstract syllogisms through the use of mental images of Venn diagrams and Euler circles (Goel et al., 2000; Goel & Dolan). Stimulation of SPL may thus have impaired abstract and incongruent reasoning by disrupting spatial processing. In contrast, congruent reasoning performance where semantic-based heuristics are sufficient to

The findings are largely consistent with the dual-process theory of reasoning, which proposes the existence of two different reasoning systems in humans: a belief-based heuristic system; and a logic-based analytic system. In our study, the left IFG appears to correspond to the heuristic system, while bilateral SPLs are part of the analytic system. The right IFG may play a role in blocking the belief-based heuristic system (left IFG) in solving incongruent reasoning trials. So, our rTMS study could offer an insight about functional roles of distributed brain systems in human deductive reasoning by utilizing the rTMS

In the present chapter, we briefly reviewed recent neuroimaging studies of human deductive reasoning, especially focusing on relatively new imaging technique: functional near-infrared spectroscopy (fNIRS) and repetitive transcranial magnetic stimulation (rTMS). A series of studies in our laboratory successfully provided evidence which is consistent with recent dual-process theory of reasoning. The dual-process theory proposed belief-based heuristic system and a logic-based analytic system. The heuristic system is assumed to

**3.2 The role of SPL in abstract reasoning** 

significantly affect abstract reasoning trials.

solve the problem was unimpaired.

approach.

**4. Conclusion** 

We found that right IFC stimulation significantly impaired reasoning performance in incongruent but not congruent trials, enhancing the belief-bias effect. This is consistent with the findings of previous neuroimaging studies using fMRI and fNIRS. In the belief-bias reasoning paradigm, semantic information processing should interfere with reasoning performance in incongruent trial, while facilitating it in congruent trials. Subjects were therefore required to inhibit semantic processing to resolve the conflicts in reasoning. When rTMS inhibited the inhibitory function of the right IFC, subjects could not respond correctly in incongruent trials, enhancing belief-bias responses.

De Neys & Franssens (2009) recently investigated the detailed nature of the inhibition process in belief-bias reasoning. In their experiments, subjects performed a lexical decision task after solving the deductive reasoning task which involved congruent and incongruent trials. They found that incongruent reasoning delayed lexical decisions regarding the target word that were relevant to the cued heuristic beliefs. Interestingly, no significant difference was apparent between congruent and incongruent reasoning trials for unrelated words. That is, the accessibility of unrelated words was unaffected. This suggests that the inhibition process is focused in nature and is specifically targeted at cued beliefs, not at semantic processing in general.

Fig. 4. Stimulation sites in rTMS experiments (IFG: inferior frontal gyrus, SPL: superior parietal lobule, BA: Broadman area).

In contrast, left IFC stimulation impaired congruent reasoning performance, while paradoxically facilitating incongruent reasoning performance. As a result, the belief-bias effect was eliminated. The left IFC is generally known to be associated with verbal or semantic processing in a wide variety of tasks, including the semantic decision task (Devlin et al., 2003), verbal fluency task (Costafreda et al., 2006), and sentence comprehension task (Zhu et al., 2009). Subjects whose left IFC was impaired by rTMS did not suffer from interference by irrelevant semantic processing, resulting in elimination of belief-bias effect. This study thus demonstrated for the first time the roles of the left and right IFC in beliefbias reasoning using an rTMS approach.

#### **3.2 The role of SPL in abstract reasoning**

42 Advances in Brain Imaging

We found that right IFC stimulation significantly impaired reasoning performance in incongruent but not congruent trials, enhancing the belief-bias effect. This is consistent with the findings of previous neuroimaging studies using fMRI and fNIRS. In the belief-bias reasoning paradigm, semantic information processing should interfere with reasoning performance in incongruent trial, while facilitating it in congruent trials. Subjects were therefore required to inhibit semantic processing to resolve the conflicts in reasoning. When rTMS inhibited the inhibitory function of the right IFC, subjects could not respond correctly

De Neys & Franssens (2009) recently investigated the detailed nature of the inhibition process in belief-bias reasoning. In their experiments, subjects performed a lexical decision task after solving the deductive reasoning task which involved congruent and incongruent trials. They found that incongruent reasoning delayed lexical decisions regarding the target word that were relevant to the cued heuristic beliefs. Interestingly, no significant difference was apparent between congruent and incongruent reasoning trials for unrelated words. That is, the accessibility of unrelated words was unaffected. This suggests that the inhibition process is focused in nature and is specifically targeted at cued beliefs, not at semantic

Fig. 4. Stimulation sites in rTMS experiments (IFG: inferior frontal gyrus, SPL: superior

In contrast, left IFC stimulation impaired congruent reasoning performance, while paradoxically facilitating incongruent reasoning performance. As a result, the belief-bias effect was eliminated. The left IFC is generally known to be associated with verbal or semantic processing in a wide variety of tasks, including the semantic decision task (Devlin et al., 2003), verbal fluency task (Costafreda et al., 2006), and sentence comprehension task (Zhu et al., 2009). Subjects whose left IFC was impaired by rTMS did not suffer from interference by irrelevant semantic processing, resulting in elimination of belief-bias effect. This study thus demonstrated for the first time the roles of the left and right IFC in belief-

in incongruent trials, enhancing belief-bias responses.

processing in general.

parietal lobule, BA: Broadman area).

bias reasoning using an rTMS approach.

Tsujii et al. (2011a) examined the effect of IFC stimulation on abstract reasoning trials in which semantic content was lacking (e.g. "All P are B"), as well as content reasoning trials which involved the congruent and incongruent trials. In contrast of the incongruent reasoning performance, we did not find the significant IFC stimulation effect on abstract reasoning performance. Right IFC stimulation impaired only incongruent trials. These findings suggest that the right IFC may not the neural locus of the analytic reasoning system. Rather, the right IFC may play a role in blocking the belief-based heuristic system (left IFC) in solving incongruent reasoning trials. On the other hand, individuals need not actively inhibit the heuristic processing on abstract trials, so right IFC stimulation did not significantly affect abstract reasoning trials.

 So, where is the neural locus responsible for abstract reasoning performance? Tsujii et al (2011a) magnetically stimulated SPL (superior parietal lobule: BA = 7). In contrast to the IFC stimulation, bilateral SPL stimulation significantly impaired abstract reasoning performance. This is consistent with previous fMRI studies which showed that the abstract reasoning performance significantly activated the SPL region (Goel et al., 2000; Goel & Dolan, 2001; Knauff et al., 2002, 2003). In general, SPL is associated with spatial processing based on evidence from fMRI (Takahama et al., 2010; Thakral & Slotnick, 2009), neurological patients (Ferber & Danckert, 2006; Shinoura et al., 2009) and TMS studies (Hamidi et al., 2008, 2009). Some authors have claimed that cognitive processes of constructing and manipulating spatially organized mental models are essential for deductive reasoning (Johnson-Laird, 1999, 2001). The mental models are a form of representation that can be spatial but more abstract. Phenomenological reports in the reasoning literature often have suggested that subjects may solve abstract syllogisms through the use of mental images of Venn diagrams and Euler circles (Goel et al., 2000; Goel & Dolan). Stimulation of SPL may thus have impaired abstract and incongruent reasoning by disrupting spatial processing. In contrast, congruent reasoning performance where semantic-based heuristics are sufficient to solve the problem was unimpaired.

The findings are largely consistent with the dual-process theory of reasoning, which proposes the existence of two different reasoning systems in humans: a belief-based heuristic system; and a logic-based analytic system. In our study, the left IFG appears to correspond to the heuristic system, while bilateral SPLs are part of the analytic system. The right IFG may play a role in blocking the belief-based heuristic system (left IFG) in solving incongruent reasoning trials. So, our rTMS study could offer an insight about functional roles of distributed brain systems in human deductive reasoning by utilizing the rTMS approach.

#### **4. Conclusion**

In the present chapter, we briefly reviewed recent neuroimaging studies of human deductive reasoning, especially focusing on relatively new imaging technique: functional near-infrared spectroscopy (fNIRS) and repetitive transcranial magnetic stimulation (rTMS). A series of studies in our laboratory successfully provided evidence which is consistent with recent dual-process theory of reasoning. The dual-process theory proposed belief-based heuristic system and a logic-based analytic system. The heuristic system is assumed to

Neural Mechanisms for Dual-Process Reasoning: Evidence from the Belief-Bias Effect 45

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operate rapidly and automatically, whereas operations of the analytic system are believed to be slow and demanding of computational resources. Our fNIRS findings could demonstrate the attention-demanding and time-consuming properties of the right IFC activities. In addition, our rTMS studies showed that the left IFG appears to correspond to the heuristic system, while bilateral SPLs are part of the analytic system. The right IFG may play a role in blocking the belief-based heuristic system (left IFG) in solving incongruent reasoning trials. Although there are several limitations of fNIRS and rTMS, we believe they are useful to examine the neural substrates of logical reasoning process.

#### **5. Acknowledgment**

Funding for this study was provided by the fund of Grant-in-Aid for Young Scientists (B) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the fund of Center of Developmental Education and Research (CODER) of Japan, and the fund for Japan Science and Technology Agency (JST), under the Strategic Promotion of Innovative Research and Development Program.

#### **6. References**


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Funding for this study was provided by the fund of Grant-in-Aid for Young Scientists (B) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the fund of Center of Developmental Education and Research (CODER) of Japan, and the fund for Japan Science and Technology Agency (JST), under the Strategic Promotion of

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**1. Introduction**

detect brain tumors.

Neuroimaging is the branch of medicine whose purpose is to provide visual information about the structure and the anatomy of the brain. The main techniques in clinics are: *Computed Tomography* (CT), *Magnetic Resonance Imaging* (MRI), *Diffuse Optical Tomography* (DOT), *Positron*

**Functional Near Infrared Spectroscopy** 

**and Diffuse Optical Tomography** 

Matteo Caffini1, Davide Contini1, Rebecca Re1,

Lucia M. Zucchelli1, Rinaldo Cubeddu1, Alessandro Torricelli1 and Lorenzo Spinelli2 *1Dipartimento di Fisica - Politecnico di Milano, Milano 2CNR - Istituto di Fotonica e Nanotecnologie, Milano*

**in Neuroscience** 

*Italy* 

**4**

CT scanning uses X-rays crossing the sample to image sections of the specimen in study. Specimen can be a living being, a part of if (e.g. the abdomen, a knee, the head, ...) or whatever non-living object. X-rays travel ballistically inside most of the materials (living tissue included), so measuring absorption of X-rays we can guess the composition of the sample we are measuring. Changing the direction of injection of the X-rays and merging absorption data coming from multiple directions makes a planar reconstruction of the examined section of the sample possible. CT is invasive in the sense that irradiates the patient with ionizing radiation. A little dose is given to the patient during a single CT session, anyway. CT scanning of the head is typically used to detect skull fractures, brain injuries, aneurysms, strokes, brain

MRI is based on nuclear magnetic resonance principles. It uses a strong static magnetic field to align the nuclear magnetization of hydrogen atoms of water in the body and then radio frequency fields are generated to alter this magnetization alignment. Several coils mounted on the scanner are then able to detect the magnetic field produced by the altered hydrogen atom magnetization and to relate the recovery time of these short-lasting magnetic fields to the environment in which resonant hydrogen atoms lie. MRI, using non-ionizing radiation, is generally considered non-invasive for the patient and provides greater contrast between different soft tissues than CT does. Magnetic resonance images of the head are mostly used to

*Emission Tomography* (PET) and *Single Photon Emission Computed Tomography* (SPECT).

tumors and arteriovenous malformations in the brain.

