Hypersensitivity to Distractors in Fragile X Syndrome from Loss of Modulation of Cortical VIP Interneurons

Attention deficit is one of the most prominent and disabling symptoms in Fragile X syndrome (FXS). Hypersensitivity to sensory stimuli contributes to attention difficulties by overwhelming and/or distracting affected individuals, which disrupts activities of daily living at home and learning at school. We find that auditory or visual distractors selectively impair visual discrimination performance in humans and mice with FXS but not in typically developing controls. In both species, males and females were examined. Vasoactive intestinal polypeptide (VIP) neurons were significantly modulated by incorrect responses in the poststimulus period during early distractor trials in WT mice, consistent with their known role as error signals. Strikingly, however, VIP cells from Fmr1 -/- mice showed little modulation in error trials, and this correlated with their poor performance on the distractor task. Thus, VIP interneurons and their reduced modulatory influence on pyramidal cells could be a potential therapeutic target for attentional difficulties in FXS.SIGNIFICANCE STATEMENT Sensory hypersensitivity, impulsivity, and persistent inattention are among the most consistent clinical features of FXS, all of which impede daily functioning and create barriers to learning. However, the neural mechanisms underlying sensory over-reactivity remain elusive. To overcome a significant challenge in translational FXS research we demonstrate a compelling alignment of sensory over-reactivity in both humans with FXS and Fmr1 -/- mice (the principal animal model of FXS) using a novel analogous distractor task. Two-photon microscopy in mice revealed that lack of modulation by VIP cells contributes to susceptibility to distractors. Implementing research efforts we describe here can help identify dysfunctional neural mechanisms associated not only with sensory issues but broader impairments, including those in learning and cognition.

Hypersensitivity to distractors in Fragile X syndrome from loss of modulation of cortical VIP interneurons

Attention deficit is one of the most prominent and disabling symptoms in Fragile X Syndrome (FXS). Hypersensitivity to sensory stimuli contributes to attention difficulties by overwhelming and/or distracting affected individuals, which disrupts activities of daily living at home and learning at school. We find that auditory or visual distractors selectively impair visual discrimination performance in both humans and mice with FXS, but not their typically developing controls. Vasoactive intestinal polypeptide (VIP) neurons were significantly modulated by incorrect responses in the post-stimulus period during early distractor trials in WT mice, consistent with their known role as 'error' signals. Strikingly, however, VIP cells from Fmr1-/- mice showed little modulation in error trials, and this correlated with their poor performance on the distractor task. Thus, VIP interneurons and their reduced modulatory influence on pyramidal cells, could be a potential therapeutic target for attentional difficulties in FXS.

Relationships Between Iron Status, Cognitive Performance, and Smoking Cessation

Objectives

Smoking cessation research suggests that women are more likely than men to respond to financial incentives to quit smoking, despite having lower rates of smoking cessation overall. Animal models suggest that iron deficiency, which is more prevalent in women, may alter dopaminergic pathways involved in both reward processing and addiction. The present study examines the extent to which iron status impacts ability to quit smoking and performance on a battery of cognitive tasks, including tasks assessing learning and decision-making which depend on the integrity of the dopaminergic pathways.

Methods

Participants were recruited from a local smoking cessation clinic and followed for 6 months as they received counseling to quit smoking. Visits included a baseline appointment, as well as 1- and 6-month follow up visits. At each appointment, participants performed cognitive tests, including the serial reaction time task (SRT) and probabilistic selection task (PST), with concurrent EEG, then gave a small sample of blood. Smoking behavior was examined using time to relapse (TTR), which was the week (1–26) in which the participant relapsed, if relapse occurred. Iron status variables of interest were hemoglobin (Hb) and percentile of the NHANES III age- and race-adjusted distributions of serum ferritin (sFtP). Correlations examined the associations between iron status variables and reaction times (RTs) on the SRT and PST, choice behavior on PST, and TTR.

Results

TTR was positively related to sFtP (r = 0.79, P < .005). Regarding the cognitive measures, there was a nonlinear relationship between sFtP and RT for the SRT task: participants with sFtP at or below the 45th percentile had a negative relationship with RT, while those with sFtP above the 55th percentile had a positive one. Hb was negatively correlated with learning from negative consequences in the PST. In addition, RTs for high-conflict choices and correct responses had a nonlinear relationship with sFtP like that found with the SRT.

Conclusions

Variations in iron affect smoking cessation as well as cognitive performance. Being low in iron may represent an additional burden to a woman who attempts to quit smoking.

Funding Sources

TSET Health Promotion Research Center - Oklahoma Tobacco Settlement Endowment Trust (TSET; Grant # r21–02) and NCI Support Grant P30CA225520.

Your Brain Knows if You're Iron Deficient: Distinct Brain Dynamics in Iron Deficient vs. Sufficient Females in a Visual Category Learning Task

Objectives

The present study sought to determine the possibility of identifying someone as either iron deficient or sufficient based solely on brain activity, and, if possible, how quickly (based on processing time on a cognitive task) this could be done.

Methods

Both iron sufficient(IS) and iron deficient non-anemic (IDNA) females (mean age 21.1 y) learned two visual categorization tasks while concurrent EEG was acquired. Both tasks involved classifying gray-scale gabor patches on the basis of spatial frequency and orientation; one task used an easily-verbalized rule (rule-based, RB), the other required complex integration of the information (II). Moving windows (20 ms width) of EEG data from 100 electrodes were used to predict the participant's iron status using logistic regression; model form was determined using stepwise variable selection. The outcome variable was the area under the curve (AUC) of the receiver operating characteristic for the classification. We set a criterion of AUC ≥ 0.80 for successful classification performance.

Results

For both tasks, successful classification was possible before 200 ms of processing on the basis of fewer than 12 electrodes. Classification in the RB task suggested some early right lateralization in the selection of electrodes, which became more central as processing proceeded. Classification in the II task did not suggest lateralization, although there was some change to more central electrodes as processing proceeded. At each 20 ms time window, for each of the selected set of electrodes, a measure of neural efficiency was calculated as the ratio of the hazard function of the reaction time distribution and the global field power of the selected set of electrodes. This ratio can be interpreted as the amount of work accomplished per unit of energy expended. In all cases, neural efficiency for the IS females exceeded that for the IDNA females, suggesting that the efficiency with which neural energy is expended in cognitive work differs as a function of iron status.

Conclusions

Iron deficiency without anemia results in distinct patterns of brain activity early in processing that reflect reduced levels of neural efficiency, relative to females who are iron sufficient.

Funding Sources

OU Office of the Vice President for Research.