Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trialby-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.

/pdf/neurophysiological-investigation-of-the-basis-of-the-fmri-1pwsdtcobg.pdf

Neurophysiological investigation of the basis of the fMRI signal

Objective:To revise the “Clinical Practice Guidelines for the Sustained Use of Sedatives and Analgesics in the Critically Ill Adult” published in Critical Care Medicine in 2002.Methods:The American College of Critical Care Medicine assembled a 20-person, multidisciplinary, multi-institutional task f

/pdf/clinical-practice-guidelines-for-the-management-of-pain-4810wy3nml.pdf

Clinical Practice Guidelines for the Management of Pain, Agitation, and Delirium in Adult Patients in the Intensive Care Unit

Social perception from visual cues : role of the STS region

The development of functional magnetic resonance imaging (fMRI) has brought together a broad community of scientists interested in measuring the neural basis of the human mind. Because fMRI signals are an indirect measure of neural activity, interpreting these signals to make deductions about the nervous system requires some understanding of the signaling mechanisms. We describe our current understanding of the causal relationships between neural activity and the blood-oxygen-level-dependent (BOLD) signal, and we review how these analyses have challenged some basic assumptions that have guided neuroscience. We conclude with a discussion of how to use the BOLD signal to make inferences about the neural signal.

Interpreting the BOLD signal.

The good coverage and high resolution afforded by functional magnetic resonance imaging (fMRI) make it an excellent tool for the noninvasive imaging of the human brain. Equally interesting, however, is the use of this technique in animal studies using high magnetic fields. In the latter case, highly

https://www.jneurosci.org/content/jneuro/23/10/3963.full.pdf

The underpinnings of the BOLD functional magnetic resonance imaging signal.

Functional magnetic resonance imaging (fMRI) has become an essential tool for studying human brain function. Here we describe the application of this technique to anesthetized monkeys. We present spatially resolved functional images of the monkey cortex based on blood oxygenation level dependent (BOLD) contrast. Checkerboard patterns or pictures of primates were used to study stimulus-induced activation of the visual cortex, in a 4.7-Tesla magnetic field, using optimized multi-slice, gradient-recalled, echo-planar imaging (EPI) sequences to image the entire brain. Under our anesthesia protocol, visual stimulation yielded robust, reproducible, focal activation of the lateral geniculate nucleus (LGN), the primary visual area (V1) and a number of extrastriate visual areas, including areas in the superior temporal sulcus. Similar responses were obtained in alert, behaving monkeys performing a discrimination task.

Functional imaging of the monkey brain

SummaryBackground and objective:High-dose opioid anaesthesia contributes to decreasing metabolic and hormonal stress responses in patients undergoing cardiac surgery. However, the increase in context-sensitive half-life of opioids given as a high-dose regimen can affect postoperative respiratory rec

Remifentanil or sufentanil for coronary surgery: comparison of postoperative respiratory impairment.

UNLABELLED Postoperative vomiting (POV) after strabismus surgery in children results in discomfort and prolonged hospital stays. Opioids increase the incidence of POV. Remifentanil has a context-sensitive half-life of 3 to 4 min, and how this short half-life influences POV in those patients is unknown. We conducted a prospective, double-blinded study in 81 ASA status I or II children from 2 to 12 yr of age undergoing elective strabismus surgery under general anesthesia. Patients were randomized to receive either remifentanil (bolus 1 microg/kg; infusion 0.1-0.2 microg x kg(-1) x min(-1)) or fentanyl (2 microg/kg, and 1 microg/kg every 45 min). POV episodes were recorded for 25 h. Pain scores were obtained by using an objective pain scale for 60 min during recovery. The number of patients who experienced POV did not differ significantly between groups (49% vs 48%). However, in the Remifentanil group, POV episodes were significantly less frequent (0.95 vs 2.2 episodes). In contrast, fentanyl was associated with lower pain scores during the first 30 min of recovery. We conclude that children undergoing strabismus surgery under balanced anesthesia with remifentanil, compared with fentanyl, showed less frequent POV. However, early postoperative analgesia was better with fentanyl. IMPLICATIONS Opioids increase the incidence of postoperative vomiting (POV). Remifentanil is characterized by the shortest half-life of all opioids used in anesthetic practice. Therefore, we studied the effect of remifentanil on POV compared with the longer-acting opioid fentanyl in children undergoing strabismus surgery.

Heinz Guggenberger

Papers

Functional imaging of the monkey brain

Remifentanil or sufentanil for coronary surgery: comparison of postoperative respiratory impairment.

The effect of remifentanil or fentanyl on postoperative vomiting and pain in children undergoing strabismus surgery.

Effect of tracheal intubation or laryngeal mask airway™ insertion on intraocular pressure using balanced anesthesia with sevoflurane and remifentanil

Electrophysiological investigation of the BOLD signal