How does O'Brien's interrogation of Winston in the Minstry of Love relate to the destruction of rational thought as a prominent idea in the novel?

In 1984, George Orwell's ominous
vision of the near future, Winston Smith, the protagonist, finds himself in a world that
actively seeks to suppress any attempts to think independently.  As an employee of the
Ministry of Truth, Winston sees the evidence of these attempts.  As part of his job,
Winston "rectifies" past newspaper articles that provide information possibly damaging
to the Party and to the reputation of Big Brother.  In addition, Syme, a colleague,
actively works to develop a revised dictionary of Newspeak, an abbreviated language
intended to weed out any language with even shades of ambiguity in its meaning, thereby
eliminating the majority of the words in the English.  These efforts ultimately result
in filtering not only the information the general population receives about its
government and its foreign relations but also the very language in which it is
expressed.  As a result, the average person only sees what the Party wants them to see,
and the average person, having an increasingly smaller vocabulary, cannot formulate any
resistance to the Party.  They literally cannot express
themselves.

Winston is well aware of these possible
consequences when he meets Julia, someone he feels has a similar attitude toward the
Party as he does.  During their "relationship," they endanger their "freedom" by
speaking out about the Party (though semi-cautiously).  Ultimately, they are turned in
and sent to the Ministry of Love.  In O'Brien's interrogation of Winston, he seeks to
break down the foundations of Winston's knowledge.  In its place, O'Brien seeks to build
a epistemological structure based on "truths" held by the Party, with the ultimate
result being Winston's inability to question ideas put forth by the
Party. 

Orwell provides numerous instances throughout
Winston's interrogation to this effect.  Perhaps the most noteworthy is O'Brien's
ability to convince Winston to accept that "2+2=5."  This clearly runs counter to
accepted mathematical truth.  It represents the destruction of rational thought in the
sense that the possibility that "2+2=4" is not discounted, for, according
to "doublethink," one can hold contradictory ideas at the same time.  Furthermore, it
brings all of Winston's assumptions into question, replacing them with ideas without any
rational basis.  Their only basis is that the Party mandates them as truth.  The
individual's ability to reason is replaced by the will of the Party - no thought
needed.