Nonlinear Effects of Noxious Thermal Stimulation and Working Memory Demands on Subjective Pain Perception.
OBJECTIVE
A bidirectional relationship between working memory (WM) and acute pain has long been assumed, but equivocal evidence exists regarding this relationship. This study characterized the relationship between WM and acute pain processing in healthy individuals using an adapted Sternberg WM task.


METHODS
Participants completed a Sternberg task while receiving noxious thermal stimulation. Participants received a pseudorandom presentation of four different temperatures (baseline temperatures and individually determined low-, medium-, and high-temperature stimuli) and four levels of Sternberg task difficulty (0-, 3-, 6-, and 9-letter strings).


METHODS
Twenty-eight healthy participants were recruited from Stanford University and the surrounding community to complete this study.


RESULTS
A nonlinear interaction between intensity of thermal stimulation and difficulty of the Sternberg task was noted. Increased cognitive load from the Sternberg task resulted in increased perception of pain in low-intensity thermal stimulation but suppressed pain perception in high-intensity thermal stimulation. Thermal stimulation had no significant effect on participants' response time or accuracy on the Sternberg task regardless of intensity level.


CONCLUSIONS
Pain perception appears to decrease as a function of WM load only for sufficiently noxious stimuli. However, increasing noxious stimuli did not affect cognitive performance. These complex relationships may reflect a shared cognitive space that can become "overloaded" with input of multiple stimuli of sufficient intensity.
Department of Anesthesiology, Perioperative and Pain Medicine, Stanford Systems Neuroscience and Pain Laboratory, Stanford University, Palo Alto, California, USA.
John A
JA
Sturgeon
Department of Anesthesiology, Perioperative and Pain Medicine, Stanford Systems Neuroscience and Pain Laboratory, Stanford University, Palo Alto, California, USA.
Meghan M
MM
Tieu
Department of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.
Laura E
LE
Jastrzab
Department of Anesthesiology, Perioperative and Pain Medicine, Stanford Systems Neuroscience and Pain Laboratory, Stanford University, Palo Alto, California, USA.
Rebecca
R
McCue
Native American Health Center, Lutheran Medical Center, San Francisco, California, USA.
Vanisha
V
Gandhi
Department of Anesthesiology, Perioperative and Pain Medicine, Stanford Systems Neuroscience and Pain Laboratory, Stanford University, Palo Alto, California, USA.
Sean C
SC
Mackey
D059787:Acute Pain / Q000503:physiopathology* / Q000523:psychology*; D000293:Adolescent; D000328:Adult; D003071:Cognition; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008570:Memory, Short-Term; D009483:Neuropsychological Tests; D017711:Nonlinear Dynamics; D010147:Pain Measurement; D058748:Pain Perception / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D055815:Young Adult
Experimental Pain; Sternberg Task; Working Memory