Pain Disrupts Working Memory

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Pain Disrupts Working Memory

http://www.medpagetoday.com/Neurology/GeneralNeurology/tb/5684

By , Senior Staff Writer, MedPage Today

Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University

of Pennsylvania School of Medicine.

Chronic pain interferes with the brain's ability to keep information

in mind while working on other tasks that require attention,

researchers here found. Action Points

Explain to interested patients that chronic pain is known to affect

the ability to pay attention to daily tasks.

Note that this study says that the key factor is the disruption of

the working memory trace -- the ability to keep pieces of

information in mind as a person works on a task.

Although pain specialists have known for years that chronic pain

interferes with attention, it hasn't been clear which functions are

actually disrupted, according to Bruce Dick, Ph.D., and Saifudin

Rashiq, M.B., M.Sc., of the University of Alberta.

It turns out that the function affected most is the so-called

working memory trace -- the ability to maintain and mentally

manipulate a memory trace while performing the spatial working

memory task -- the researchers reported in the May issue of

Anesthesia & Analgesia.

They enrolled 24 patients, 18 of them women, from the pain center at

the University of Alberta Hospital and gave them a series of

cognitive tests both before and after they had analgesic treatment

for their pain.

Tests included:

The test of everyday attention, which profiles sustained and

selective attention.

The reading span test, which reflects the efficiency of basic

cognitive skills.

And the spatial span test, which taxes the processing and storage

components of spatial working memory.

Patients were eligible if they had a reduction of at least four

points on a numerical pain score after treatment, which might have

included epidural injection, somatic nerve blockade, pulsed

radiofrequency rhizotomy of the medial branch nerves, and trigger

point therapy.

Patients were excluded if they had a history of significant head

injury, neurological disorder, or disease known to impair attention,

the researchers said.

Using the test of everyday attention, the researchers found that a

third of the patients were not clinically impaired by their pain,

and divided the remaining 16 into two groups -- less and more

disrupted.

All patients reported pain levels significantly reduced after their

treatment (at P<0.0001).

But, the researchers reported, the pain relief had no significant

effect on measures included in the test of everyday attention,

including overall performance, selective attention, or sustained

attention.

There was also no significant difference on the reading span test,

they said.

But they did find differences on the " mirror task " of the spatial

span test. In that test, patients are asked to look at a series of

letters presented askew on a computer screen and to determine

whether each letter is in its normal orientation or a mirror image.

Patients are also told to remember what direction the top of each

letter is facing. At the end of the series, the patient must report

the direction. The test relies on the working memory trace, the

researchers said.

The unimpaired and less impaired groups performed equally well on

the mirror task, the researchers found, but the more impaired group

fared significantly worse (at P<0.05).

" Working memory trace (is) a specific cognitive process that appears

to be disrupted by chronic pain, " they concluded.

The study is limited by its small size, the researchers said, but

the statistical findings were robust.