Electrophysiology and Functional MRI in Post-Acute Mild Traumatic Brain Injury

Abstract

Symptoms persisting beyond the acute phase (>2 months) after a mild traumatic brain injury (MTBI) are often reported, but their origin remains controversial. Some investigators evoke dysfunctional cerebral mechanisms, while others ascribe them to the psychological consequences of the injury. We address this controversy by exploring possible cerebral dysfunction with functional magnetic resonance imaging (fMRI) and event-related potentials (ERP) in a group of patients during the post-acute phase. Fourteen MTBI symptomatic patients (5.7±2.9 months post-injury) were tested with fMRI and ERP using a visual externally ordered working memory task, and were compared with 23 control subjects. Attenuated blood oxygen level dependent (BOLD) signal changes in the left and right mid-dorsolateral prefrontal cortex (mid-DLPFC), the putamen, the body of the caudate nucleus, and the right thalamus were found in the MTBI group compared with the control group. Moreover, symptom severity and BOLD signal changes were correlated: patients with more severe symptoms had lower BOLD signal changes in the right mid-DLPFC. For ERP, a group×task interaction was observed for N350 amplitude. A larger amplitude for the working memory task than for the control task was found in control subjects, but not in MTBI subjects, who had weak amplitudes for both tasks. This study confirms that persistent symptoms after MTBI cannot be uniquely explained by psychological factors, such as depression and/or malingering, and indicates that they can be associated with cerebral dysfunction. ERP reveals decreased amplitude of the N350 component, while fMRI demonstrates that the more severe the symptoms, the lower the BOLD signal changes in the mid-DLPFC.

Transcranial Magnetic Stimulation-Electroencephalography Responses in Recovered and Symptomatic Mild Traumatic Brain Injury

“…None of the participants had any injury visible in conventional MRI. In accordance with previous DTI, functional MRI, and positron emission tomography studies, [5][6][7][8][9][10][11] we expected to see mTBI related changes in nTMS-EEG responses of the frontal areas, especially with nTMS of the DLPFC. We also expected to find more pronounced changes in the symptomatic participants compared with those who had recovered.…”

“…[1][2][3][4] DTI has shown altered fractional anisotropy and diffusion after mTBI in the corpus callosum, in the dorsolateral prefrontal cortex (DLPFC) region, and in frontal white matter regions. [5][6][7][8][9] Decreased resting state activity 10 and activation related blood flow response 11 have been observed in prefrontal areas in mTBI, correlating with symptom severity. These results suggest that structural damage may be present in mTBI and may explain the persistent symptoms experienced by some patients.…”

Evaluating the cognitive consequences of mild traumatic brain injury and concussion by using electrophysiology

“…Among the MTBI group, 14 patients had been included in a previous ERP and fMRI study in our laboratory. 23 The MTBI group was compared with 40 control volunteers who were their equivalent for age and sex. No control participants had a diagnosis or history of neurological and/or psychiatric conditions (including previous TBI and substance abuse) and no one used drugs known to affect cognition.…”

“…In a recent study, preliminary data on 14 patients with MTBI or concussion showed that the frontal N350 ERP wave associated with WM was abnormal when compared with control volunteers. 23 This anomaly was concurrently associated with reduced fMRI activation in the mid-DLPFC during the performance of the same externally ordered WM task. These results need to be confirmed in a larger sample of patients with different types of injury, for example motor vehicle accident and sports concussion.…”

“…This reduction has been associated with symptom severity; that is, the more severe the symptoms, the lower the activations observed in the mid-DLPFC. [14][15][16]23,24 Only a limited number of studies have used ERP during the performance of a WM task to further refine our understanding of the cognitive sequelae of MTBI. The ERP is a noninvasive method that represents the electrophysiological signal associated with stimulus perception and cognitive processes during a task.…”