It's a description of a particular kind of rigidity.
From:
http://neuro-www.mgh.harvard.edu/forum_2/ParkinsonsDiseaseF/Alittleinformation.html

Cogwheel Rigidity: Stiffness in the muscles, with a jerky quality when
arm and leg joints are repeatedly moved.

Cogwheel Rigidity: muscular rigidity that produces a ratcheted resistant
in the limbs of Parkinson's patients.

Cogwheel rigidity: When tested against passive movements, initial
resistance is felt by the examiner. This then relaxes, only to stiffen
again giving the classical 'cogwheel' or ratchet-like process seen
prominently at the wrist, elbow, or knee.

Rigidity is defined as a resistance (increased muscle tone) to passive
movement. Typical Parkinsonian rigidity is intermittent in nature, thus
its name "cogwheel rigidity." In Parkinson's Disease, the best joints to
use are the wrist and elbow. When the rigidity is subtle and difficult
to detect,one can use the Noika maneuvre to elicit an increased response
rigidity testing. (The maneuvre involves flexing the muscles of the
contralateral arm. While the rigidity is often bilateral, there is
usually one predominant side. In addition to cogwheel rigidity, there is
also generalized
rigidity affecting mostly the neck, trunk and the knees leading to a
stooped posture.

Some say patients diagnosed with essential tremors can have cogwheeling
rigidity.

Cogwheel rigidity is included in extrapyramidal signs. And you can have
extrapyramidal signs due to a reaction to drugs such as
antipsychotic/neuroleptic medications.

Beth

If it was 'TIA' you wanted to know about:

TIA = Transient Ischemic Attack

A transient (TRANS-e-ant) ischemic (is-SKI-mik) attack, called a TIA for
short, is often a warning signal of an impending stroke. Pieces of fat or
blood clots can block an artery leading to the brain. When this happens, a
part of the brain does not get enough oxygen and the symptoms of a TIA
appear. With a TIA, the artery is only blocked a short time. With a stroke,
the blockage lasts much longer, causing brain damage.

Causes
High blood pressure, diabetes, excess weight, high amounts of fat in the
blood (cholesterol), and smoking.

Signs/Symptoms

Appear suddenly, last less than 24 hours, and go away completely. Typical
signs include seeing double, loss of vision, fainting or dizziness, a weak
or numb feeling on one side of the face or body, or trouble swallowing or
speaking.

If it was the 'cogwheeling' info you wanted... I found the following:

Cogwheel Rigidity: Stiffness in the muscles, with a jerky quality when arm
and leg joints are repeatedly moved.

Cogwheel Rigidity: muscular rigidity that produces a ratcheted resistant in
the limbs of Parkinson's patients.

Cogwheel rigidity: When tested against passive movements, initial resistance
is felt by the examiner. This then relaxes, only to stiffen again giving the
classical 'cogwheel' or ratchet-like process seen prominently at the wrist,
elbow, or knee.

Rigidity is defined as a resistance (increased muscle tone) to passive
movement. Typical Parkinsonian rigidity is intermittent in nature, thus its
name "cogwheel rigidity." In Parkinson's Disease, the best joints to use are
the wrist and elbow. When the rigidity is subtle and difficult to detect,one
can use the Noika maneuvre to elicit an increased response rigidity testing.
(The maneuvre involves flexing the muscles of the contralateral arm. While
the rigidity is often bilateral, there is usually one predominant side. In
addition to cogwheel rigidity, there is also generalized
rigidity affecting mostly the neck, trunk and the knees leading to a stooped
posture.

Some say patients diagnosed with essential tremors can have cogwheeling
rigidity.

Cogwheel rigidity is included in extrapyramidal signs. And you can have
extrapyramidal signs due to a reaction to drugs such as
antipsychotic/neuroleptic medications.

Hope that helps.

N.
http://com5.runboard.com/balzheimers