Reduced Sensitivity to Background Reward Underlies Apathy After Traumatic Brain Injury: Insights From an Ecological Foraging Framework.

BACKGROUND: Altered reward processing is increasingly recognised as a crucial mechanism underpinning apathy in many brain disorders. However despite its clinical relevance, little is known about the mechanisms of apathy following moderate-to-severe traumatic brain injury (TBI). In real-life situations, reward representations encompass both foreground (gains from current activity) and background (potential gains from the broader environment) elements. This latter variable provides a crucial set-point for switching behaviour in many naturalistic settings. We hypothesised apathy post-TBI would be associated with disrupted background reward sensitivity. METHODS: We administered a computer-based foraging task to 45 people with moderate-to-severe TBI (20 with apathy, 39 males) and 37 matched controls. Participants decided when to leave locations (patches) where foreground reward rates depleted at differing rates, to pursue greater rewards from other patches in the environment, which had either a high or low background reward rate. Primary analysis was performed using linear mixed effects models, with patch leaving time the dependent variable. RESULTS: Findings showed a significant interaction between apathy and background reward sensitivity, driven by apathetic TBI participants not altering patch-leaving decisions as environmental reward rate changed. In contrast, although TBI was associated with reduced sensitivity to changing foreground rewards, this did not vary as a function of apathy. CONCLUSIONS: These results provide the first evidence directly linking disrupted background reward processing to apathy in any brain disorder. They identify a novel mechanism for apathy following moderate-to-severe TBI, and point towards novel interventions to improve this debilitating complication of head injury.

Contributions of intrinsic and extrinsic reward sensitivity to apathy: Evidence from traumatic brain injury.

OBJECTIVE: Apathy is a key feature of traumatic brain injury (TBI). However, mechanisms underlying apathy are poorly understood. Evidence suggests that changes in reward may be a crucial factor. Rewards can come from two important sources: extrinsic reward (e.g., money) and intrinsic reward (e.g., enjoyment). Here, we used an experimental paradigm to examine the contributions of intrinsic-extrinsic reward sensitivity to apathy post-TBI and neurocognitive processes associated with these reward processing components. METHOD: Fifty-seven patients with TBI (TBI with clinical/severe apathy [TBI + sA], TBI with subclinical/moderate apathy [TBI + mA] and TBI without apathy [TBI-A] groups), and 30 healthy individuals completed the "birthday-gift task." In the "intrinsic reward" condition, participants chose to "go" to collect the gift or "wait" for the same gift to be delivered. In the "extrinsic reward" condition, the task was identical, however, participants received monetary incentives when choosing "going" instead of "waiting." The Montreal Cognitive Assessment was utilized for cognitive examination. RESULTS: A smaller proportion of people in the TBI + sA group had high sensitivity to both intrinsic and extrinsic rewards than the TBI + mA, TBI-A and healthy comparison groups. The TBI+sA group also perceived the "go" option on the intrinsic reward condition as more effortful and made fewer "go" decisions on the extrinsic condition. Attention was the only predictor of intrinsic reward sensitivity, whereas executive functioning, attention and group predicted extrinsic reward. CONCLUSION: This study demonstrates the relationship between intrinsic-extrinsic reward hyposensitivity and apathy post-TBI. These results may be integrated into future trials to improve apathy in clinical practice. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Modifying thin-film composite forward osmosis membranes using various SiO2 nanoparticles for aquaculture wastewater recovery.

This paper describes the fabrication, modification, and evaluation of the performance of thin-film composite (TFC) forward osmosis (FO) membranes for lab-scale aquaculture wastewater recovery using various fumed silica (SiO2) nanoparticles. The active polyamide (PA) layers of these membranes were novelly modified using different types of pretreated SiO2 nanoparticles [virgin SiO2, dried SiO2, and 3-aminopropyltriethoxysilane (APTES)-modified SiO2] and concentrations (0.05, 0,1, 0,2, and 0.4 wt%) to improve the membrane hydrophilicity with minimum particle agglomeration. Results show that the APTES-SiO2 modified membrane had the highest water flux and selectivity, followed by the dried-SiO2 modified membrane. The APTES coupling agent notably reduced the SiO2 aggregation on the membrane surface and improved membrane hydrophilicity. Consequently, high permeate flux and an acceptable reverse solute flux were observed. The optimal SiO2 concentration for PA modification was 0.1 wt% for all the nanoparticle types. The virgin and APTES-SiO2 modified membranes were used for aquaculture wastewater recovery. The water recovery rate reached 47% in 84 h when using the APTES-SiO2 modified membrane, while it reached only 26% in 108 h when using the virgin membrane. With a suitable design of the filtration apparatus and choice of draw solution (DS), the prepared novel TFC-FO membrane containing APTES-modified SiO2 can be used for recycling aquaculture wastewater into the DS, which can then be reused for other purposes.