Intraoperative Brain Mapping by Cortico-Cortical Evoked Potential

Intracortical mechanisms of single pulse electrical stimulation (SPES) evoked excitations and inhibitions in humans

Cortico-cortical evoked potentials (CCEPs) elicited by single-pulse electric stimulation (SPES) are widely used to assess effective connectivity between cortical areas and are also implemented in the presurgical evaluation of epileptic patients. Nevertheless, the cortical generators underlying the various components of CCEPs in humans have not yet been elucidated. Our aim was to describe the laminar pattern arising under SPES evoked CCEP components (P1, N1, P2, N2, P3) and to evaluate the similarities between N2 and the downstate of sleep slow waves. We used intra-cortical laminar microelectrodes (LMEs) to record CCEPs evoked by 10 mA bipolar 0.5 Hz electric pulses in seven patients with medically intractable epilepsy implanted with subdural grids. Based on the laminar profile of CCEPs, the latency of components is not layer-dependent, however their rate of appearance varies across cortical depth and stimulation distance, while the seizure onset zone does not seem to affect the emergence of components. Early neural excitation primarily engages middle and deep layers, propagating to the superficial layers, followed by mainly superficial inhibition, concluding in a sleep slow wave-like inhibition and excitation sequence.

Cortico-cortical evoked potential and language mapping: A meta-analysis

PURPOSE

The purpose of this meta-analysis was to determine the best available evidence for the use of cortico-cortical evoked potential (CCEP) for language mapping.

METHODS

PubMed/Medline/Google Scholar/Cochrane and Scopus electronic databases were searched for articles using CCEP for language mapping. CCEP data was obtained including the area of the cortex generating CCEP, resection data, and post-resection language outcomes. Inclusion criteria were clinical articles reporting the use of CCEP in language regions of the brain, reporting language outcomes and whether there was final resection of the cortex, studies with more than five patients, and studies in either English or Spanish. Review articles, systematic reviews, meta-analyses, or case series with less than five patients were excluded.

RESULTS

Seven studies with a total of 59 patients were included in this meta-analysis. The presence of CCEPs from stimulation of Broca's area or posterior perisylvian region in the resection predicts language deficits after surgery. The diagnostic odds ratio shows values greater than 0 perioperatively (0.69-5.82) and after six months (1.38-11), supporting a high likelihood of a language deficit if the presence of CCEPs from stimulation of Broca's area or posterior perisylvian region are included in the resection and vice versa. The True Positive rate varied between 0.38 and 0.87. This effect decreases after six months to 0.61 (0.30-0.86). However, the True Negative rate increased from 0.53 (0.32-0.79) to 0.71 (0.55-0.88).

CONCLUSION

This meta-analysis supports the utility of CCEP to predict the probability of having long-term language deficits after surgery. .

Differential cortical network engagement during states of un/consciousness in humans

What happens in the human brain when we are unconscious? Despite substantial work, we are still unsure which brain regions are involved and how they are impacted when consciousness is disrupted. Using intracranial recordings and direct electrical stimulation, we mapped global, network, and regional involvement during wake vs. arousable unconsciousness (sleep) vs. non-arousable unconsciousness (propofol-induced general anesthesia). Information integration and complex processing we`re reduced, while variability increased in any type of unconscious state. These changes were more pronounced during anesthesia than sleep and involved different cortical engagement. During sleep, changes were mostly uniformly distributed across the brain, whereas during anesthesia, the prefrontal cortex was the most disrupted, suggesting that the lack of arousability during anesthesia results not from just altered overall physiology but from a disconnection between the prefrontal and other brain areas. These findings provide direct evidence for different neural dynamics during loss of consciousness compared with loss of arousability.

Large-scale brain networks and intra-axial tumor surgery: a narrative review of functional mapping techniques, critical needs, and scientific opportunities

In recent years, a paradigm shift in neuroscience has been occurring from "localizationism," or the idea that the brain is organized into separately functioning modules, toward "connectomics," or the idea that interconnected nodes form networks as the underlying substrates of behavior and thought. Accordingly, our understanding of mechanisms of neurological function, dysfunction, and recovery has evolved to include connections, disconnections, and reconnections. Brain tumors provide a unique opportunity to probe large-scale neural networks with focal and sometimes reversible lesions, allowing neuroscientists the unique opportunity to directly test newly formed hypotheses about underlying brain structural-functional relationships and network properties. Moreover, if a more complete model of neurological dysfunction is to be defined as a "disconnectome," potential avenues for recovery might be mapped through a "reconnectome." Such insight may open the door to novel therapeutic approaches where previous attempts have failed. In this review, we briefly delve into the most clinically relevant neural networks and brain mapping techniques, and we examine how they are being applied to modern neurosurgical brain tumor practices. We then explore how brain tumors might teach us more about mechanisms of global brain dysfunction and recovery through pre- and postoperative longitudinal connectomic and behavioral analyses.

Neuromonitoring of the language pathways using cortico-cortical evoked potentials: a systematic review and meta-analysis

Cortico-cortical evoked potentials (CCEPs) are a surge in activity of one cortical zone caused by stimulation of another cortical zone. Recording of CCEP may be a useful method of intraoperative monitoring of the brain pathways, particularly of the language-related tracts. We aimed to conduct a systematic review and meta-analysis, dedicated to the clinical question: Does the CCEP recording effectively predict the postoperative speech deficits in neurosurgical patients? We conducted language-restricted PubMed, Google Scholar, Scopus, and Cochrane database search for eligible studies of CCEP published until March 2021. There were 4 articles (3 case series and 1 case report), which met our inclusion/exclusion criteria. A total of 32 patients (30 cases of tumors and 2 cavernomas) included in the analysis were divided into two cohorts - quantitative and qualitative, in accordance with the method of evaluating changes in the amplitude of CCEP after the lesion resection and postoperative alterations in speech function. Quantitative variables were studied using the Spearman rank correlation coefficient. Categorical variables were compared in groups by Fisher's exact test. We found a strong positive correlation between the decrease in the N1 wave amplitude and the severity of postoperative speech deficits (quantitative cohort: r = 0.57, p = 0.01; qualitative cohort: p = 0.02). Thus, the CCEP method using the N1 wave amplitude as a marker enables to effectively predict postoperative speech outcomes. Nevertheless, the low level of evidence for the included works indicated the necessity for additional research on this issue.

Diagnosis of children with attention-deficit/hyperactivity disorder (ADHD) comorbid autistic traits (ATs) by applying quantitative magnetic resonance imaging techniques

OBJECTIVE

To explore the feasibility of applying quantitative magnetic resonance imaging techniques for the diagnosis of children with attention-deficit/hyperactivity disorder (ADHD) comorbid autistic traits (ATs).

METHODS

A prospective study was performed by selecting 56 children aged 4-5 years with ADHD-ATs as the study group and 53 sex- and age-matched children with ADHD without ATs as the control group. All children underwent magnetic resonance scans with enhanced T2^*- weighted magnetic resonance angiography (ESWAN), 3D-PCASL, and 3D-T1 sequences. Iron content and cerebral blood flow parameters were obtained via subsequent software processing, and the parameter values in particular brain regions in both groups were compared and analyzed to determine the characteristics of these parameters in children with ADHD-ATs.

RESULTS

Iron content and cerebral blood flow in the frontal lobe, temporal lobe, hippocampus, and caudate nucleus of children with ADHD-ATs were lower than those of children with ADHD without ATs (p < 0.05). Iron content and CBF values in the frontal lobe, temporal lobe and caudate nucleus could distinguish children with ADHD-ATs from those without ATs (AUC > 0.5, p < 0.05).

CONCLUSIONS

Quantitative magnetic resonance techniques could distinguish children with ADHD-ATs.

TRIAL REGISTRATION

This study protocol was registered at the Chinese clinical trial registry (ChiCTR2100046616).

Pediatric awake epilepsy surgery: Intraoperative language mapping utilizing digital video gaming and electrocorticography

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Awake craniotomy for language mapping in children requires a specific perioperative strategy.

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Extraoperative language cortical mapping using a grid electrode provides more optimal setting that reduces anxiety and improves compliance.

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The utilization of video game familiar to the pediatric patient reduce anxiety and enhance cooperation during awake language cortical mapping.

Intraoperative functional language mapping is vital to minimize the risks associated with surgical removal of the seizure onset zone in selected patients with epilepsy. In children, this method has been reported extraoperatively by the placement of invasive electrodes to map the language area and monitor epileptic activity. It is difficult from a technical standpoint to perform an awake craniotomy and language mapping in young children under 10 years of age. Here we report a 9-year-old boy suffering from drug-resistant non-lesional epilepsy who underwent extraoperative and intraoperative electrical stimulation with successful identification of Broca’s language area. Electrocorticography (ECOG) was applied intraoperatively in a continuous manner utilizing grid electrodes before the skin opening. We found that the use of visual digital video games facilitated extraoperative and intraoperative cortical mapping. Cortical language inhibition by electrical stimulation was elicited at an amplitude of 7 mA (100 μs single-phase duration and 50 Hz pulse width). Resection of the seizure onset zone was completed safely. The post-resection ECOG revealed the disappearance of epileptogenic electrographic discharges at the seizure onset contacts and at other involved contacts in the epileptogenic zone. After surgery, the child recovered well with no language deficits and remained seizure-free. The child remembered only the video game test that was performed intraoperatively. This report highlights safety strategies for awake language mapping in pediatrics and the importance of the perioperative use of a visual digital video game and continuous ECOG, in addition to the use of targeted language cortex stimulation to facilitate faster and safer intraoperative language mapping under awake conditions in this age group.

Cognitive and Emotional Mapping With SEEG

Mapping of cortical functions is critical for the best clinical care of patients undergoing epilepsy and tumor surgery, but also to better understand human brain function and connectivity. The purpose of this review is to explore existing and potential means of mapping higher cortical functions, including stimulation mapping, passive mapping, and connectivity analyses. We examine the history of mapping, differences between subdural and stereoelectroencephalographic approaches, and some risks and safety aspects, before examining different types of functional mapping. Much of this review explores the prospects for new mapping approaches to better understand other components of language, memory, spatial skills, executive, and socio-emotional functions. We also touch on brain-machine interfaces, philosophical aspects of aligning tasks to brain circuits, and the study of consciousness. We end by discussing multi-modal testing and virtual reality approaches to mapping higher cortical functions.