Multiple linear regression, fMRI
To put it simply, it will give you a equation (less error relative to data-set presumed to be correct equation). Depending on data-set, equation has constants value for each variables which will provides the ratio of one variable with other variables.
You might find equation on similar format as this: 

y = (b0 + b1.x1 + b2.x2 + b3.x3) + c


where x1  , x2 , x3 can be different characteristics (as variables which can be IQ, age, working momory, etc.) and b0 , b1, b2, b3 are the constant calculated from given data-set. 

You can find exact value of y or x1 or x2 or x3 if you have exact value of other 3 variables. 

Lets say, it was the data-set provided to an android/robot as in sci-fi movies; that android/robot will make it's decision based on this equation as law/fact/pattern and judge a person response time (if every other variables are known) or IQ (if every other variables are known) etc. by this equation.

There is also a lot of details in this.

Note: This logic will only practical with Multiple Linear Regression Method.