In the following passage some of the words have been deleted. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.
A recent study that (1) ______ people’s brains at different points in their work day (2) ______high-demand tasks which require intense, constant concentration can lead to build-up of a (3) ______ toxic chemical called glutamate. Normally used to (4) ______ signals from nerve cells, in large quantities glutamate alters the (5) ______ of a brain region involved in planning and decision making, the lateral prefrontal cortex (lPFC).

Select the most appropriate option to fill in blank number 5.