In this work, the relationship between the cortical thickness and motor cortex excitability was studied in patients with AD or MCI and in healthy controls. A significant negative correlation was found between the cortical thickness and EFMT on the sensorimotor cortex, on the precuneus and on the cuneus. The relationship appeared to differ between the study groups depending on the cortical area: in AD subjects the correlation was weakest on the sensorimotor cortex whereas in MCI subjects on the cuneus. In healthy controls the EFMT did not correlate with the cortical thickness in any of the ROIs. Resting motor threshold along with the EFMT reflects the excitability of a central core of neurons and combines the excitability of individual neurons with their local density. In more details, the rMT depends on the excitability of cortico-cortical axons and is influenced by the diameter, coherence and density of these axons that connect the stimulated motor cortex with other cortical areas. TMS given at intensity close to the rMT predominantly evokes I waves which are considered to arise from transsynaptic activation of corticospinal neurons. By increasing the intensity of the magnetic stimulus, both the maximum of the induced electrical field and the size of the directly influenced brain volume increase. The amplitude of a MEP is known to increase with increasing stimulus intensity, evidence that stronger stimuli recruit more corticospinal neurons. Therefore, in order to produce a measurable MEP, a sufficient number of neurons must be excited. This can be achieved by increasing the stimulation intensity because the increase of intensity activates neurons in a larger area and at the same time activates also those neurons with a higher activation threshold. Moreover, the stimulating current is most effective and stable when directed according to local columnar structure, i.e., perpendicular to the central sulcus, increasing the net number of synchronously activated neurons. Our results are in line with this proposal since the cortical thickness on the sensorimotor cortex was found to correlate negatively with the EFMT when all subjects were included in the analysis. A negative correlation means that the thinner the cortex, the stronger the stimulation intensity needed to produce MEPs. Since a thick cortex contains more neurons, a smaller area needs to be activated to stimulate the same amount of neurons, and thus weaker stimulus intensity is sufficient to elicit MEPs. A similar negative correlation between the cortical thickness and the EFMT corresponding the thenar muscle rMT was found on the precuneus and the cuneus. The precuneus is among other things NVP-BEZ235 915019-65-7 involved in motor imagery, in coordination of motor behaviour as well as in reaction time reduction in a button press task. Furthermore, resting-state functional connectivity analysis has revealed that the precuneus is functionally connected with the motor cortex. In addition, the cuneus is involved in inhibitory control and also in generating finger movements based on gaze position. Therefore, the precuneus and the cuneus might be involved in some way in cortical excitability and the process of generating MEPs.