Understanding the neural basis of consciousness is fundamental to neuroscience research. Disruptions in cortico-cortical connectivity have been suggested as a primary mechanism of unconsciousness. By using a novel combination of positron emission tomography and functional magnetic resonance imaging, we studied anesthesia-induced unconsciousness and recovery using the α2-agonist dexmedetomidine. During unconsciousness, cerebral metabolic rate of glucose and cerebral blood flow were preferentially decreased in the thalamus, the Default Mode Network (DMN), and the bilateral Frontoparietal Networks (FPNs). Cortico-cortical functional connectivity within the DMN and FPNs was preserved. However, DMN thalamo-cortical functional connectivity was disrupted. Recovery from this state was associated with sustained reduction in cerebral blood flow and restored DMN thalamo-cortical functional connectivity. We report that loss of thalamo-cortical functional connectivity is sufficient to produce unconsciousness.DOI: http://dx.doi.org/10.7554/eLife.04499.001

The International League Against Epilepsy (ILAE) classification of focal seizures uses recall of experiences post‐ictally to assess for awareness and not ictal responsiveness to external stimuli, stating that responsiveness is often not tested. We investigated how clinicians assess for seizure awareness by administering an online survey. We found that most respondents use both responsiveness and recall to assess for awareness in the clinic (78%) and in the epilepsy monitoring unit (72%). Furthermore, 60% of respondents believe that the ILAE recommends using both measures. Given our results, we believe that using both responsiveness and recall would provide a more practical classification of impaired consciousness in focal seizures.

Background and Purpose— Lacunar strokes are subcortical infarcts with small size and high disability rates, largely due to injury of the corticospinal tract in the internal capsule (IC). Current rodent models of lacunar infarcts are created based on stereotactic coordinates. We tested the hypothesis that better understanding of the somatotopy of the IC and guiding the lesion with electrical stimulation would allow a more accurate lesion to the forelimb axons of the IC. Methods— We performed electrophysiological motor mapping and viral tracing to define the somatotopy of the IC of Sprague Dawley rats. For the lesion, we used an optrode, which contains an electrode to localize forelimb responses and an optical fiber to deliver light. The infarct was induced when light activated the photothrombotic agent Rose Bengal, which was administered systemically. Results— We found largely a separate distribution of the forelimb and hindlimb axons in the IC, both by microstimulation mapping and tract tracing. Microstimulation-guided IC lesions ablated the forelimb axons of the IC in rats and caused lasting forelimb impairments while largely preserving the hindlimb axons of the IC and surrounding gray matter. Conclusions— Stimulation guidance enabled selective and reproducible infarcts of the forelimb axons of the IC in rats. Visual Overview— An online visual overview is available for this article.

Objective. The current International League Against Epilepsy (ILAE) guidelines classify focal seizures based on awareness, defined as successful postictal recall of ictal experiences, and exclude the use of responsiveness during seizures for classification. One reason for this exclusion is that responsiveness was thought to not be commonly tested during seizures. Our goal was to determine whether, in at least some settings, responsiveness testing during seizures is relatively common. Methods. We assessed how often responsiveness and recall were each evaluated in patients with focal epilepsy undergoing surface and intracranial EEG-video monitoring. We performed this evaluation by retrospectively reviewing video recordings from 121 seizures from 48 patients during their stay in the epilepsy monitoring unit between September 2012 and November 2019.Results. We found that responsiveness during seizures was tested more frequently than recall of ictal events after seizures. Of 121 seizures in 48 patients, responsiveness was tested in 101 seizures, whereas recall was tested in only 38. Significance. Evaluating if consciousness is impaired during seizures is of critical importance for guiding recommendations for people with epilepsy, such as whether it is safe for them to drive or operate machinery. The ILAE classification guidelines are intended to be broadly useful, but our findings demonstrate that at least in one important clinical setting, responsiveness was used more commonly than recall to evaluate patients during focal seizures. Although our preliminary findings should be replicated in a larger sample and in other patient groups, they suggest that responsiveness testing during focal seizures might be relatively common in at least some clinical practice settings. With further study, this may lead to a re-evaluation of criteria for classifying focal seizures to include both responsiveness and recall of experiences during seizures, as both may provide important information to guide clinical care.