A review of magnetic resonance imaging and diffusion tensor imaging findings in mild traumatic brain injury

Mild traumatic brain injury (mTBI), also referred to as concussion, remains a controversial diagnosis because the brain often appears quite normal on conventional computed tomography (CT) and magnetic resonance imaging (MRI) scans. Such conventional tools, however, do not adequately depict brain injury in mTBI because they are not sensitive to detecting diffuse axonal injuries (DAI), also described as traumatic axonal injuries (TAI), the major brain injuries in mTBI. Furthermore, for the 15 to 30 % of those diagnosed with mTBI on the basis of cognitive and clinical symptoms, i.e., the "miserable minority," the cognitive and physical symptoms do not resolve following the first 3 months post-injury. Instead, they persist, and in some cases lead to long-term disability. The explanation given for these chronic symptoms, i.e., postconcussive syndrome, particularly in cases where there is no discernible radiological evidence for brain injury, has led some to posit a psychogenic origin. Such attributions are made all the easier since both posttraumatic stress disorder (PTSD) and depression are frequently co-morbid with mTBI. The challenge is thus to use neuroimaging tools that are sensitive to DAI/TAI, such as diffusion tensor imaging (DTI), in order to detect brain injuries in mTBI. Of note here, recent advances in neuroimaging techniques, such as DTI, make it possible to characterize better extant brain abnormalities in mTBI. These advances may lead to the development of biomarkers of injury, as well as to staging of reorganization and reversal of white matter changes following injury, and to the ability to track and to characterize changes in brain injury over time. Such tools will likely be used in future research to evaluate treatment efficacy, given their enhanced sensitivity to alterations in the brain. In this article we review the incidence of mTBI and the importance of characterizing this patient population using objective radiological measures. Evidence is presented for detecting brain abnormalities in mTBI based on studies that use advanced neuroimaging techniques. Taken together, these findings suggest that more sensitive neuroimaging tools improve the detection of brain abnormalities (i.e., diagnosis) in mTBI. These tools will likely also provide important information relevant to outcome (prognosis), as well as play an important role in longitudinal studies that are needed to understand the dynamic nature of brain injury in mTBI. Additionally, summary tables of MRI and DTI findings are included. We believe that the enhanced sensitivity of newer and more advanced neuroimaging techniques for identifying areas of brain damage in mTBI will be important for documenting the biological basis of postconcussive symptoms, which are likely associated with subtle brain alterations, alterations that have heretofore gone undetected due to the lack of sensitivity of earlier neuroimaging techniques. Nonetheless, it is noteworthy to point out that detecting brain abnormalities in mTBI does not mean that other disorders of a more psychogenic origin are not co-morbid with mTBI and equally important to treat. They arguably are. The controversy of psychogenic versus physiogenic, however, is not productive because the psychogenic view does not carefully consider the limitations of conventional neuroimaging techniques in detecting subtle brain injuries in mTBI, and the physiogenic view does not carefully consider the fact that PTSD and depression, and other co-morbid conditions, may be present in those suffering from mTBI. Finally, we end with a discussion of future directions in research that will lead to the improved care of patients diagnosed with mTBI.

Electrophysiological and diffusion tensor imaging evidence of delayed corollary discharges in patients with schizophrenia

BACKGROUND

Patients with schizophrenia (SZ) characteristically exhibit supranormal levels of cortical activity to self-induced sensory stimuli, ostensibly because of abnormalities in the neural signals (corollary discharges, CDs) normatively involved in suppressing the sensory consequences of self-generated actions. The nature of these abnormalities is unknown. This study investigated whether SZ patients experience CDs that are abnormally delayed in their arrival at the sensory cortex.

METHOD

Twenty-one patients with SZ and 25 matched control participants underwent electroencephalography (EEG). Participants' level of cortical suppression was calculated as the amplitude of the N1 component evoked by a button press-elicited auditory stimulus, subtracted from the N1 amplitude evoked by the same stimulus presented passively. In the three experimental conditions, the auditory stimulus was delivered 0, 50 or 100 ms subsequent to the button-press. Fifteen SZ patients and 17 healthy controls (HCs) also underwent diffusion tensor imaging (DTI), and the fractional anisotropy (FA) of participants' arcuate fasciculus was used to predict their level of cortical suppression in the three conditions.

RESULTS

While the SZ patients exhibited subnormal N1 suppression to undelayed, self-generated auditory stimuli, these deficits were eliminated by imposing a 50-ms, but not a 100-ms, delay between the button-press and the evoked stimulus. Furthermore, the extent to which the 50-ms delay normalized a patient's level of N1 suppression was linearly related to the FA of their arcuate fasciculus.

CONCLUSIONS

These data suggest that SZ patients experience temporally delayed CDs to self-generated auditory stimuli, putatively because of structural damage to the white-matter (WM) fasciculus connecting the sites of discharge initiation and destination.

Interleukin-1 stimulates glucose transport in rat adipose cells. Evidence for receptor discrimination between IL-1 beta and IL-1 alpha

The effect of interleukin 1 (IL-1) on glucose transport activity in isolated rat adipose cells was examined. IL-1 beta stimulated 3-O-methylglucose (3OMG) transport in a time and dose dependent manner. This effect appears to be due to increased maximal transport velocity (Vmax) of the carrier. Addition of insulin and IL-1 beta resulted in an additive stimulation of transport, suggesting different mechanisms. IL-1 alpha had no effect on glucose transport. Glu-4, a relatively inactive IL-1 beta analogue in most cells, stimulated glucose uptake in a time and dose dependent manner with kinetics indistinguishable from those of IL-1 beta.

Effect of manganese deficiency on insulin binding, glucose transport and metabolism in rat adipocytes

The effect of manganese deficiency on insulin binding, glucose transport and metabolism in isolated adipose cells from Sprague-Dawley rats was investigated. Offspring from Mn-sufficient female rats fed 45 micrograms Mn/g diet (control) and from Mn-deficient (Mn-) female rats fed 1 microgram Mn/g diet were used in these studies. Both basal and insulin-stimulated 3-O-methylglucose transport in isolated adipose cells was significantly lower in Mn- rats, averaging 40% and 50% of control values, respectively. Kinetic analysis of glucose transport demonstrated a lower maximal transport velocity (Vmax) for glucose in adipose cells from Mn- rats compared to controls. No differences in the Km for glucose uptake were observed between the two groups. Insulin-stimulated glucose oxidation to CO2 and conversion to triglycerides was lower in isolated adipose cells from Mn- rats compared to controls. Mn- animals had fewer insulin receptors per cell compared to controls, although no differences in insulin receptor affinity were observed between the two groups. These data suggest that Mn deficiency affects glucose transport and metabolism in the adipose cell. The apparent defect lies distal to the insulin receptor and probably reflects a decreased number of glucose transporters in adipose tissue of Mn- rats.