2. Methods used to study our brain and it's cognitive function

120 years ago the brain was too complex to work on over those years operating on the brain was proven to be difficult having very little knowledge and understanding of the brain. 
Many studies/research have been conducted in measuring the brain function and structure. 
Somatosensory homunculus also known as “the little man inside the brain”, puts forward an understanding of a distorted model of a human to reflect the human body parts occupying on the somatosensory cortex and the motor cortex. Body parts such as lips, hand, feet and sex organs are very sensitive therefore have more sensory neurons so the cortex has correspondingly large lips, hands, feet and genitals. 
Single case studies have enabled researchers to study specific damaged brain areas and the resulting behaviour, however it did have its advantages and disadvantages. Although it allowed us to understand the role of a brain region, single case studies cannot conside unknown previous levels of functioning and it is subject to individual differences. 
There are several types of methods used in terms of brain surgery. From the times of labotamy, things have certainly changed and surgeons and scientists have more knowledge in terms of localization. There are four different types of methods used: 1) Behavioural Studies 2) Lesion Studies 3) Haemodynamic Studies (PET+FMRI), 4) Electromagnetic  (MEG and EEG). 
1) Electroencephalography (EEG) is the recording of electrical activity along the scalp. Although it is non-ivasive and has a high a high temporal resolution it has a significantly lower spatial resolution and it is unclear what EEG changes signifies.
2) Event-related potentials (ERP) is a measure of brain responses that is directly the result of a thought or perception and it is critcised for being a poorly understood underlying mechanism.
3) Position Emission Tomography (PET) provide a measure of brain function through the measuring oxygen consumption, blood flow and glucose metabolism. Blood flow vbeing the most reliable of the measurements. It is performed by using a gamma ray detector and provides a 3D representation  of local activity. It is however very expensive and has a poor temporal resolution. 
4) Magnetic Resonance Imaging (MRI) provides a detailed internal structures. Although it is non ivasive and non toxic  the radio frequencies must be shielded. 
5) FMRI measures blood oxygen levels, again it is non ivasive and non toxic and has an excellent spatial resolution, however the analysis is complex and it is very expensive to use. 
6) Transcranial Magnetic Stimulation (TMS) allows the modulation of cortical activity by passing alternating magnetic fields across the scalp. It induces electrical currents in the cortex increasing or decreasing its excitability. 

There are many pros and cons to these methodologies and over the last 150 years surgeons have progressed tremendous amounts at a human cost which raises the question does the end justify the means?