Pain Does Not Follow the Boxcar Model: Temporal Dynamics of the BOLD fMRI Signal During Constant Current Painful Electric Nerve Stimulation

The temporal dynamics of the blood oxygen level–dependent (BOLD) signal, especially for painful stimulations, is not completely understood. In this study, the BOLD signal response to a long painful electrical stimulation (a continuous painful stimulation of 2 minutes) is directly compared to that of a short painful stimulation (four 30-second periods of painful stimulation interleaved with 30-second rest) in an effort to further probe the relationship between the temporal dynamics of the BOLD signal during constant-intensity pain stimulation. Time course analysis showed that both stimulation protocols produced 3 similarly timed peaks in both data sets, suggesting an early and delayed BOLD response to painful stimulation initiation, and a response related to stimulus termination. Despite the continuous stimulation, the BOLD signal returned to baseline in the 2-minute task. Even with this signal discrepancy, however, the activation maps of the 2 pain tasks differed only slightly, suggesting that the bulk of the activation is determined by the sharp rise in BOLD signal with stimulus onset. These findings imply that the BOLD signal response time course is not directly reflective of pain perception.     

Functional Magnetic Resonance Imaging Studies of Pain: An Investigation of Signal Decay during and across Sessions

Background: Several investigations into brain activation caused by pain have suggested that the multiple painful stimulations used in typical block designs may cause attenuation over time of the signal within activated areas. The effect this may have on pain investigations using multiple tasks has not been investigated. The signal decay across a task of four repeating pain stimulations and between two serial pain tasks separated by a 4-min interval was examined to determine whether signal attenuation may significantly confound pain investigations.

Methods: The characteristics of the brain activation of six subjects were determined using whole brain blood oxygenation level-dependent functional magnetic resonance imaging on a 1.5-T scanner. Tasks included both tingling and pain induced by transcutaneous electrical stimulation of the median nerve. The average group maps were analyzed by general linear modeling with corrected cluster P values of less than 0.05. The time courses of individual voxels were further investigated by analysis of variance with P values of less than 0.05.

Results: Significant differences between pain and tingling were found in the ipsilateral cerebellum, contralateral thalamus, secondary somatosensory cortex, primary somatosensory cortex, and anterior cingulate cortex. Highly significant signal decay was found to exist across each single pain task, but the signal was found to be restored after a 4-min rest period.     

Peripheral intravenous catheter infiltration: anesthesia providers do not adhere to their own ideas of best practice

Study ObjectiveTo survey anesthesia providers for their opinion on “best practice” in perioperative peripheral intravenous catheter (PIV) management, and to determine if they follow those opinions.DesignSurvey instrument.SettingAcademic medical center.Subjects266 United States (U.S.) anesthesia provider respondents (attending anesthesiologists, anesthesiology residents, anesthesia assistants, certified registered nurse-anesthetists and student registered nurse-anesthetists).MeasurementsBetween May 2009 and October 2010 a national survey was distributed to individuals who provide intraoperative anesthesia care to patients. Results were gathered via the SurveyMonkey database.Main Results266 anesthesia providers from across the U.S. took part in the survey. The majority (70%) had less than 5 years’ experience. Nearly 90% of respondents cared for a patient with an intravenous catheter infiltration at some point during their training; 7% of these patients required medical intervention. Intravenous assessment and documentation practices showed great variability. Management and documentation of PIVs was more aggressive and vigilant when respondents were asked about “best practice" than about actual management.ConclusionThere is no commonly accepted standard for management and documentation of PIVs in the operating room. From our survey, what providers think is “best practice" in the management and documentation of PIVs is not what is being done.     

An fMRI study of semantic priming: modulation of brain activity by varying semantic distances.

OBJECTIVE: Our purpose was to study the effect of semantic priming at varying semantic distances on brain activation during a lexical decision experiment, using functional magnetic resonance imaging (fMRI). BACKGROUND: Neuroimaging studies have demonstrated decreased brain activation for primed versus unprimed stimuli in language areas due to semantic priming, suggesting facilitated semantic retrieval. However, the effect of varying semantic distances on brain activation has not been studied. Therefore we examined direct and indirect priming effects on cerebral activation to provide information regarding spread of activation in the semantic network. METHODS: Participants were presented with closely, distantly, and unrelated word pairs during fMRI, and asked to make a lexical decision on the second word. RESULTS: Behavioral measurements demonstrated significant priming effects for all semantic distances. Imaging results showed modulation of brain activation due to different semantic relationships in the left inferior frontal gyrus, bilateral middle frontal gyrus and anterior temporal lobe, and consisted of decreased magnitude of activation when primed stimuli were processed compared with unprimed stimuli, with the greatest effect observed for closely related words. CONCLUSIONS: This study demonstrates graduated effects of semantic priming on fMRI in semantic but not attentional brain regions, contributing to explain how semantic knowledge is organized and retrieved. These findings support the network model for organization of the semantic lexicon.     

The effects of L-dopa on the functional magnetic resonance imaging response of patients with amblyopia: a pilot study.

PURPOSE: We investigated the effects of a single dose of levodopa (L-dopa) on the level and extent of visual cortex activation of subjects with amblyopia and normal subjects using blood oxygenation level-dependent functional magnetic resonance imaging (fMRI). SUBJECTS AND METHODS: Six patients with amblyopia and 9 control patients were recruited. A baseline fMRI session was followed by a second session 90 minutes after the dose of L-dopa. Visual stimuli included vertical sinusoidal gratings with spatial frequencies of 1 and 2 cpd that were counterphased at 4 Hz. Stimuli were presented monocularly and binocularly. The fMRI response was characterized by the total volume and the average level of activation within the occipital cortex. An interocular absolute difference (IDIF) was defined in terms of said measures for between-population analysis of monocular data. RESULTS: After the administration of L-dopa, visual acuity improved significantly ( P = 0.026) from 0.72 +/- 0.21 (mean +/- SD) to 0.64 +/- 0.24 LogMAR in the amblyopic eye, although remaining the same in the dominant eye and in the eyes of control subjects. The response to L-dopa was found to be population-specific, as indicated by a significant treatment-by-population interaction for the volume of activation IDIF ( P = 0.018) measure: subjects with amblyopia exhibited a post-treatment increase in the volume of activation IDIF whereas control subjects showed a less prominent decrease. This post-treatment increase of IDIF in subjects with amblyopia may be explained by the decrease in the volume of activation found for the amblyopic eye after L-dopa ( P = 0.038). No L-dopa-related activation changes were detected for dominant eye or binocular stimulation in the amblyopic group, and no change was detected in control subjects. CONCLUSION: L-dopa elicits a population-specific modulation of the fMRI response, namely, a reduced total volume of activation from the amblyopic eye despite improvement in visual acuity.