Sagar Jilka

Damage to the Salience Network and Interactions with the Default Mode Network

Interactions between the Salience Network (SN) and the Default Mode Network (DMN) are thought to be important for cognitive control. However, evidence for a causal relationship between the networks is limited. Previously, we have reported that traumatic damage to white matter tracts within the SN predicts abnormal DMN function. Here we investigate the effect of this damage on network interactions that accompany changing motor control. We initially used fMRI of the Stop Signal Task to study response inhibition in humans. In healthy subjects, functional connectivity (FC) between the right anterior insula (rAI), a key node of the SN, and the DMN transiently increased during stopping. This change in FC was not seen in a group of traumatic brain injury (TBI) patients with impaired cognitive control. Furthermore, the amount of SN tract damage negatively correlated with FC between the networks. We confirmed these findings in a second group of TBI patients. Here, switching rather than inhibiting a motor response: (1) was accompanied by a similar increase in network FC in healthy controls; (2) was not seen in TBI patients; and (3) tract damage after TBI again correlated with FC breakdown. This shows that coupling between the rAI and DMN increases with cognitive control and that damage within the SN impairs this dynamic network interaction. This work provides compelling evidence for a model of cognitive control where the SN is involved in the attentional capture of salient external stimuli and signals the DMN to reduce its activity when attention is externally focused.

How do earworms start? Classifying the everyday circumstances of Involuntary Musical Imagery

Involuntary Musical Imagery (INMI) or “earworms” describes the experience whereby a tune comes into the mind and repeats without conscious control. The present article uses an inductive, generative, grounded theory-based qualitative analysis to classify reports of everyday INMI circumstances, and creates graphical models that determine their relative frequency within two population samples; listeners to the BBC radio station 6 Music and an online survey. Within the two models, four abstract categories were defined that described the characteristics of the circumstances surrounding the onset of INMI episodes; Music exposure, Memory triggers, Affective states, and Low attention states respectively. We also note the variety of musical media by which exposure to a tune results in an INMI episode and discuss the impact of musical engagement on INMI experiences. The findings of the present study are considered within a framework of involuntary retrieval theory from both the autobiographical and semantic memory literatures. In addition, the results highlight the potential facilitative effects of varying affective and attentional states on INMI episodes.

Pituitary dysfunction after blast traumatic brain injury: The UK BIOSAP study.

Pituitary dysfunction is a recognized consequence of traumatic brain injury (TBI) that causes cognitive, psychological, and metabolic impairment. Hormone replacement offers a therapeutic opportunity. Blast TBI (bTBI) from improvised explosive devices is commonly seen in soldiers returning from recent conflicts. We investigated: (1) the prevalence and consequences of pituitary dysfunction following moderate to severe bTBI and (2) whether it is associated with particular patterns of brain injury.

Experiencing earworms: An interview study of Involuntary Musical Imagery

Involuntary musical imagery (INMI) is a ubiquitous cognitive phenomenon. The present study comprises six intensive interviews that examine the subjective phenomenology of INMI for individuals of varying musical experience. Grounded theory analysis was used to establish themes regarding both the form and feelings ascribed to INMI episodes. All the respondents felt that their INMI experiences had high fidelity including some complex musical arrangements. INMI form could be unstable over time according to cognitive demands. Individuals with musical experience reported concurrent sensations of visual and motor imagery as well as involuntary extemporizations of their INMI. Motivators for positive and negative appraisals of INMI were identified such as nostalgia and entertainment, and repetitive cycling with loss of control, respectively. We discuss interpretations from auditory memory theory and develop hypotheses for future INMI empirical investigation.

Prevalence and correlates of vitamin D deficiency in adults after traumatic brain injury

Traumatic brain injury (TBI) is a major cause of long‐term disability with variable recovery. Preclinical studies suggest that vitamin D status influences the recovery after TBI. However, there is no published clinical data on links between vitamin D status and TBI outcomes. The aim was to determine the (i) prevalence of vitamin D deficiency/insufficiency, and associations of vitamin D status with (ii) demographic factors and TBI severity, and with (iii) cognitive function, symptoms and quality of life, in adults after TBI.

Serum insulin-like growth factor-I levels are associated with improved white matter recovery after traumatic brain injury

Traumatic brain injury (TBI) is a common disabling condition with limited treatment options. Diffusion tensor imaging measures recovery of axonal injury in white matter (WM) tracts after TBI. Growth hormone deficiency (GHD) after TBI may impair axonal and neuropsychological recovery, and serum insulin‐like growth factor‐I (IGF‐I) may mediate this effect. We conducted a longitudinal study to determine the effects of baseline serum IGF‐I concentrations on WM tract and neuropsychological recovery after TBI.

Serum IGF-I levels are associated with improved white matter recovery after TBI

Traumatic brain injury (TBI) is a common disabling condition with limited treatment options. Diffusion tensor imaging measures recovery of axonal injury in white matter (WM) tracts after TBI. Growth hormone deficiency (GHD) after TBI may impair axonal and neuropsychological recovery, and serum insulin‐like growth factor‐I (IGF‐I) may mediate this effect. We conducted a longitudinal study to determine the effects of baseline serum IGF‐I concentrations on WM tract and neuropsychological recovery after TBI.