**Step 2:**

Second, a correlation analysis of spatially registered resting state and/or taskbased functional MRI recorded in the same person is then accomplished to construct a voxel-wise all-to-all *functional connectivity* matrix for the human brain.

*Perspective Chapter: Functional Human Brain Connectome in Deep Brain Stimulation (DBS)… DOI: http://dx.doi.org/10.5772/intechopen.109855*

**Figure 1.** *Using the human brain connectome to localize symptoms [27].*

#### **Step 3:**

Subsequently, a cluster analysis of correspondences between the structural and functional connectivity matrix obtained from the last two steps is carried out. With that, the human brain regions of consistent structure-function relationships can be found.

In this way, it is possible for us to map out the human connectome. To further improve the quality of the connectome, we may need to compare the mapped network with animal models to look for correspondences and deviations. Also, the predictions generated from the structural-functional connectivity matrix can be validated with specific stimulation techniques.

## **4. Normative connectome and the human connectome project (HCP)**

Even though human connectome is a big step in enhancing localization in the nervous system, it is time-consuming, expensive and may be exhausting to the patients because they have to go through a lengthy process of image acquisitions with functional MRI and diffusion-weighted MRI. In fact, in a clinical imaging context, the human connectomes can be studied with either individual MRI data or the MRI data from a group of individuals. The latter approach gives rise to an idea known as a *normative connectome*, which is described as an average or generalized wiring diagram of the human brain [27].

Normative connectome can be useful in those who fail to obtain their own connectomes [27]. For instance, in PD patients with severe tremor or dyskinesia, they may not be able to obtain good-quality MRI images without motion artifacts. Besides, in those patients with cerebral lesions such as cerebrovascular accident, they may not be able to obtain their own connectome even if they can tolerate the long procedure of image acquisition. It is because with previous cerebral insults, that specific region(s) in the brain may have been damaged, thereby disrupting the cerebral circuitry focally and making it impossible to map out the functional connectivity accurately. Nevertheless, normative connectome, which is obtained from group MRI data, cannot provide each individual information of connectivity of his own brain, and may not reflect his actual situation. It can vary with age, gender, body mass index and neurological diseases [41–46].

As such, research studying normative connectome of the human brain has grown in number over the last five to ten years and the Human Connectome Project (HCP) is a good example. It is a large-scale project conducted in the U.S. to examine the human brain circuits and their relationship to behavior in a large population of healthy adults at a macroscopic level [27, 47, 48]. Clinical and neuroimaging information obtained in this project were listed out as follows [47–49].

