Infrared thermography mapping plus neuronavigation target location in an eloquent area cavernoma resection

Background: Safety and efficacy are irrebuttable goals in neurosurgery. Methods: We performed a subcortical cavernoma resection in an eloquent area, where we recorded and compared the maximal and minimal brain temperature measured by an infrared thermographic camera and thermometer with the neuronavigation (NN) target location and real anatomical lesion location. Results: The hottest cortical point correlated to the subcortical cavernoma location. The NN located the target at 10 mm away from the hottest point. Conclusion: More studies are needed to better understand the thermic radiation of the brain in health and in disease, but we believe that evaluating brain temperature, it could be possible to improve accuracy in neurosurgery and generate more knowledge about brain metabolism in vivo.

Thermography mapping patterns in temporal lobe epilepsy surgery

Background: In several epilepsy etiologies, the macroscopic appearance of the epileptogenic tissue is identical to the normal, which makes it hard to balance between how much cytoreduction or disconnection and brain tissue preservation must be done. A strategy to tackle this situation is by evaluating brain metabolism during surgery using infrared thermography mapping (IrTM). Methods: In 12 epilepsy surgery cases that involved the temporal lobe, we correlated the IrTM, electrocorticography, and neuropathology results. Results: Irritative zones (IZ) had a lower temperature in comparison to the surrounding cortex with normal electric activity (difference in temperature (ΔT) from 1.2 to 7.1, mean 3.40°C standard deviation ± 1.61). The coldest zones correlated exactly with IZ in 9/10 cortical dysplasia (CD) cases. In case 3, the coldest area was at 1 cm away from the IZ. In 10/10 dysplasia cases (cases 1–4, 6–11), there was a radial heating pattern originating from the coldest cortical point. In 2/2 neoplasia cases, the temporal lobe cortical temperature was more homogeneous than in the CD cases, with no radial heating pattern, and there were no IZ detected. In case 8, we found the coldest IrTM recording in the hippocampus, which correlated to the maximal irritative activity recorded by strip electrodes. The ΔT is inversely proportional to epilepsy chronicity. Conclusion: IrTM could be useful in detecting hypothermic IZ in CD cases. As the ΔT is inversely proportional to epilepsy chronicity, this variable could affect the metabolic thermic patterns of the human brain.

Uniform spatial spread of population activity in primate parafoveal V1

What are the shape and size of the region in primate V1 that processes information from a single point in visual space? This region, a fundamental property termed cortical point image (CPI) ( McIlwain 1986 ), represents the minimal population of V1 neurons that can be activated by a visual stimulus and therefore has important implications for population coding in the cortex. Previous indirect attempts to measure the CPI in macaque V1 using sparse microelectrode recordings resulted in conflicting findings. Whereas some early studies suggested that CPI size is constant throughout V1 (e.g., Hubel and Wiesel 1974 ), others have reported large changes in CPI size in parafoveal V1 (e.g., Van Essen et al. 1984 ). To resolve this controversy, we used voltage-sensitive dye imaging in V1 of fixating monkeys to directly measure the subthreshold CPI and several related properties across a range of parafoveal eccentricities. We found that despite large changes in other properties of the retinotopic map, the subthreshold CPI is approximately constant and extends over ∼6 × 8 mm2. This large and invariant CPI ensures a uniform representation of each point in visual space, with a complete representation of all visual features in V1, as originally proposed by Hubel and Wiesel (1974) . In addition, we found several novel and unexpected asymmetries and anisotropies in the shapes of the CPI and the population receptive field. These results expand our understanding of the representation of visual space in V1 and are likely to be relevant for the representations of stimuli in other sensory cortical areas.

Varying the Degree of Single-Whisker Stimulation Differentially Affects Phases of Intrinsic Signals in Rat Barrel Cortex

Varying the degree of single-whisker stimulation differentially affects phases of intrinsic signals in rat barrel cortex. . Neurophysiol. 81: 692–701, 1999. Using intrinsic signal optical imaging (ISI), we have shown previously that the point spread of evoked activity in the rat barrel cortex in response to single-whisker stimulation encompasses a surprisingly large area. Given that our typical stimulation consists of five deflections at 5 Hz, the large area of evoked activity might have resulted from repetitive stimulation. Thus in the present study, we use ISI through the thinned skull to determine whether decreasing the degree of single-whisker stimulation decreases the area of the cortical point spread. We additionally outline a protocol to quantify stimulus-related differences in the temporal characteristics of intrinsic signals at a fine spatial scale. In 10 adult rats, whisker C2 was stimulated randomly with either one or five deflections delivered in a rostral-to-caudal fashion. Each deflection consisted of a 0.5-mm displacement of the whisker as measured at the point of contact, 15 mm from the snout. The number of whisker deflections did not affect the area or peak magnitude of the cortical point spread based on the intrinsic signal activity occurring from 0.5 up to 1.5 s poststimulus onset. In contrast, the magnitude and time course of intrinsic signal activity collected after 1.5-s poststimulus onset did reflect the difference in the degree of stimulation. Thus decreasing the degree of stimulation differentially affected the early and late phases of the evoked intrinsic signal response. The implications of the present results are discussed in respect to probable differences in the signal source underlying the early versus later phases of evoked intrinsic signals.

On the instability of a cortical point

Slight and transient differences in the depth of narcosis, in the freedom of blood supply, and in the temperature of the preparation modify reactions obtained from stimulation of the motor area in the cortex cerebri with a facility and to a degree not met in the study of purely spinal or decerebrate reflexes. The observer, when first attempting to decipher the rules exhibited by the reflex activities of a spinal or of a decerebrate preparation, naturally turns first to those results which lend themselves best, by regularity and harmony, to exact formulation. Occasional exceptions as they arise are reserved for examination in the future. In a similar manner, the codification of those responses which are obtained with the greatest reliability from the several cortical points is what at first chiefly concerns the observer in the study of the elicitation of different movements from different points in the cortex cerebri.