**2.4 Discussion**

#### **2.4.1 Baseline: At rest or during the neutral task**

A previous study (Coull & Nobre, 1998) used the resting state as the baseline to be consistent with previous reports using visual fixation controls (Corbetta et al., 1993). In addition, the neutral condition engages attention and orients attention between two spatial locations and two temporal intervals.

In this study, we focused on the activation without finger movement by asking the subjects to click the reaction key ten times during rest. We compared the activation in each task with the resting state. With the exception of the visual and auditory cortices, no significant activation occurred in the N task. Therefore, we used the N task as the baseline to examine

Early Detection of Alzheimer's Disease with Cognitive Neuroscience Methods 45

severe stages of the disease lose their ability to perform the simplest of tasks encountered in their daily routine. Mild cognitive impairment is a clinical disorder that afflicts elderly individuals and is characterised by memory impairment that does not interfere significantly with their daily living (Petersen et al., 1999). In addition, MCI is a major risk factor in the development of AD (Petersen, 2004). Currently, the mini-mental state examination (MMSE) (Folstein et al., 1975) and the clinical dementia rating (CDR) system (Morris, 1993) are used as references to help a physician determine whether a person diagnosed with memory

The somatosensory system is a diverse sensory system comprising the receptors and processing centres to produce the sensory modalities. Tactile spatial discrimination is one of the major manual learning and memory skills of humans. Tactile spatial acuity at the fingertips varies significantly with age (Stevens & Patterson, 1995). Previous studies have suggested two possible effects of this variation on tactile spatial discrimination: (a) differences in the central pathways of the brain leading to tactile perception and (b) differences in afferent innervation density between younger and older subjects. However, the differences in the ability to discriminate tactile angles between healthy older individuals

To differentiate two different objects by touch, humans need to store the spatial information of the first object in their working memory and then compare the spatial construction of the first object to that of the second. This procedure activates a diverse cerebral network that primarily includes areas involved with the initial processing of skin indentations (i.e., primary and secondary somatosensory cortex) (Blatow et al., 2007), the high-class areas for computation and elaborate reconstruction of shapes (i.e., part of the intraparietal sulcus) and the prefrontal cortex (Bodegård et al., 2001), which is activated for tactile working memory processing. We hypothesise that having abnormal somatosensory information processing contributes to the functional decline of tactile shape discrimination in patients with MCI and

In this section from our recent study (Yang et al., 2010), we characterised tactile shape discrimination deficits in patients with MCI and AD and assessed whether tactile shape discrimination impairment could distinguish patients with MCI and AD from NC individuals. To allow a controlled study of shape, we used a restricted working definition of shape that can be applied to any object with angles (Wu et al., 2010) and to examine the ability to identify differences in raised angles in MCI and AD patients and the NC individuals. The results indicated that the decline in tactile angle discrimination in patients

Three groups of right-handed subjects (i.e., NC, MCI and AD) consented to participate in the study. Handedness was confirmed with the Edinburgh Handedness Inventory (EHI) (Oldfield, 1971). All MCI and AD patients were recruited from the Okayama University Hospital, Japan, and all subjects had no deficits in motor and sensory systems and deep tendon reflexes. They also reported no loss of tactile sensation or any unusual experiences with haptic input. All subjects signed informed consent forms, and the experiments were

performed in accordance with a protocol approved by the Okayama University.

problems has AD.

and patients with MCI and AD has not been reported.

with MCI and AD compared to the NC group was significant.

AD compared to NC individuals.

**3.2 Methods 3.2.1 Subjects** 

the activation that resulted from spatial or temporal cues. The activation in VS–VN in the frontal (BA4/6/47) and parietal (BA7/40) cortices was similar to previous studies (Coull & Nobre, 1998; Nobre et al., 2000). The VT–VN revealed bilateral activation in the parietal cortex (BA7) (Coull et al., 2000).

The right hemisphere bias for spatial orientation in this study was consistent with a previous report (Coull & Nobre, 1998). Therefore, we conclude that visual orienting attention uses a frontal–parietal neutral network for visual spatial orienting attention but uses the parietal cortex for visual temporal attention.

#### **2.4.2 The cue used in the auditory orienting attention task**

We used a visual cue in the auditory orienting attention tasks, whereas no cue was used in previous studies (Zatorre et al., 1999; Degerman et al., 2006). When comparing the activation in those studies, we found common areas in both the parietal (BA7) and frontal (BA6) cortices. In this study, the prefrontal cortex showed less activation than in previous studies (Zatorre et al., 1999; Degerman et al., 2006), and when examining the RT in the auditory orienting attention task that revealed a slow reaction, we noted that the magnetic resonance machine made a sound that drew the subjects' attention. Therefore, the AT–AN showed no activation for the same problem. One study (Schubotz et al., 2003) mentioned an auditory temporal attention task, with activation of the inferior temporal gyrus (BA20) and fusiform gyrus (BA37). In that study, only one temporal interval was used, which was different than this study.

Some studies (Loose et al., 2003; Johnson & Zatorre, 2006) used both visual and auditory stimuli to measure the attention to the stimuli feature and divided attention. Although no spatial or temporal attention task was applied using a similar task, they revealed similarities between the activation in response to visual and auditory tasks. We postulate that if the proper auditory stimulus was used in the auditory orienting attention task, neutral network activation and visual orienting attention might be demonstrated.
