Impact of Handgun Ownership and Biological Sex on Startle Reactivity to Predictable and Unpredictable Threats

Abstract

Extant literature suggests that many individuals obtain firearms because they perceive the world as unsafe and believe that firearm ownership increases physical protection. Converging evidence suggests that firearm owners are vulnerable to uncertainty and experience chronic anticipatory anxiety in daily life; however, biological sex is thought to potentially moderate this association. Studies have yet to examine this hypothesis using objective markers of anticipatory anxiety. The present study therefore examined the impact of handgun ownership and biological sex on psychophysiological reactivity to predictable (P-) and unpredictable (U-) threat (N = 133). Male and female adult participants were classified into two groups: a) individuals who do not currently own any handguns (n = 52), and b) individuals who currently own one or more handguns (n = 81). Startle eyeblink potentiation was recorded as an index of aversive reactivity during a well-validated threat-of-shock paradigm designed to probe anticipatory anxiety (during U-threat) and fear (during P-threat). Results revealed no main effect of group on startle reactivity to P- or U-threat. Females displayed greater startle reactivity to threat (P- and U-) compared with males. The main effect was qualified by a significant group x biological sex interaction. Male handgun owners exhibited greater startle to U-threat, but not P-threat, relative to non-handgun owners. There was no effect of group on startle reactivity in females. Findings revealed that biological sex and threat type influenced threat reactivity. Male handgun owners displayed increased sensitivity to stressors that are uncertain, which may reflect an objective mechanism related to firearm ownership.

1. Introduction

Firearm ownership is significantly higher in the United States than other Western nations, with approximately 93 firearms per 100 citizens in the U.S. compared to an average of 25 firearms per 100 citizens in other Western countries (Hepburn et al., 2007). Approximately 30,000-40,000 Americans die from firearms each year and up to 100,000 are nonfatally injured (Swanson et al., 2015; Xu et al., 2018). Nearly two-thirds of all firearm-related deaths are suicides and more than half of all suicides involve firearms (Kochanek et al., 2019; Xu et al., 2020). Firearm access in the home is also associated with increased risk for domestic homicide and homicide more broadly (Anestis and Houtsma, 2018; Brent, 2001; Campbell et al., 2003; Dahlberg et al., 2004). It is critical we better understand factors that contribute to violent deaths among firearm owners and identify modifiable risk factors to mitigate these outcomes.

Extant literature suggests that firearm acquisition is related to perceptions that the world is unsafe and that having a firearm increases their protection. Indeed, research has repeatedly shown that self-protection is the most common reason for firearm ownership and is strongly associated with overgeneralized perceptions of the world as a dangerous place (Parker et al., 2017; Stroebe et al., 2017). More specifically, fear of being a crime victim and having previously been a crime victim are associated with firearm ownership and plans to purchase a firearm in the near future (Arthur, 1992; Hill et al., 1985; Kleck et al., 2011; Turner et al., 2016; Wallace, 2017). Additionally, data supports the motivating role of anticipatory anxiety in firearm acquisition but reductions in anxiety following firearm possession have not been observed (Hauser and Kleck, 2013). In fact, firearm possession, as well as losing a firearm, may increase subjective anxiety and behavioral reactivity in response to environmental threats (Hauser and Kleck, 2013; Taylor et al., 2017; Witt and Brockmole, 2012). Firearm owners also report feeling safer when they believe that others are carrying firearms, too, despite the increased risk for injury and mortality associated with firearm possession (Brent et al., 1993; Kellerman et al., 1993; Shepperd et al., 2018). Together, these findings suggest that firearm ownership and possession may contribute to increased threat vigilance and subjective anxiety, which in turn reinforces firearm possession (Grupe and Nitschke, 2013).

Although many firearm owners, particularly handgun owners, report self-protection as their primary reason for ownership, research findings to date yield mixed evidence about whether or not firearm owners exhibit enhanced anticipatory anxiety compared with non-owners (Dowd-Arrow et al., 2019; Kleck et al., 2011; Pierre, 2019; Warner and Thrash, 2020). Exaggerated threat expectancies, or the cognitive bias towards inflating the probability and cost of future negative events, is a key component of anticipatory anxiety that contributes to increased behavioral reactivity. For example, we recently found that individuals intending to purchase a firearm in the next 12 months reported significantly higher threat expectancies than those who did not intend to purchase (Bryan et al., 2022). Additionally, from a data sample collected shortly after the COVID-19 pandemic began, we found that individuals intending to acquire a firearm in the next 12 months were less tolerant of uncertainty, endorsed exaggerated threat expectancies, and experienced more severe COVID-19 specific fears, as well as more likely to already own firearms and to have purchased firearms during the beginning of the pandemic (Anestis and Bryan, 2021). Altogether, these studies suggest that firearm owners and prospective owners may be vulnerable to higher threat expectancies given uncertainty and experience chronic hypervigilance, with purchasing and owning firearms serving as a coping strategy.

To date, research has relied exclusively on self-report and has yet to examine differences in psychophysiological reactivity to uncertainty between firearm owners and non-owners. One laboratory paradigm designed to objectively measure response to uncertainty is the no threat-predictable threat-unpredictable threat task (NPU; Schmitz and Grillon, 2012). This task measures response to temporally predictable and unpredictable threat, two overlapping but separable aversive states (Barlow, 2000; Davis, 2006; Grillon et al., 2004). The unpredictable (U) threat component measures an individual’s level of generalized apprehension and sustained hypervigilance, while the predictable (P) threat component elicits a discrete fight-or-flight response (Davis et al., 2010; Grillon et al., 2004; Nelson and Hajcak, 2017; Wieser et al., 2016). Given that arousal and hypervigilance are hallmark features of anticipatory anxiety elicited by U-threat, we hypothesized that handgun owners may exhibit selectively increased reactivity to U-threat during the NPU paradigm compared to non-handgun owners.

Furthermore, reactivity to uncertainty may vary by other characteristics of firearm owners. Biological sex, in particular, is noteworthy given research showing sex differences in reasons for firearm ownership, firearm-related worries, victimization experiences, and risk reduction strategies (Borgogna et al., 2022; Logan and Lynch, 2021; Logan and Walker, 2017; May et al., 2010; Wintemute, 2011; Wolfson et al., 2020). Specifically, females are more likely to own a firearm solely for protection, have a personal history of victimization, and have a greater fear of future victimization (Warner, 2020). Given the aforementioned connection between protective motives, exaggerated threat expectancies, and behavioral reactivity, we hypothesized that the difference in U-threat reactivity between handgun owners and non-handgun owners may be particularly evident for females.

The present study aimed to examine the impact of firearm ownership on reactivity to temporally predictable and unpredictable threat, as well as potential sex differences. Adults aged 18-65 participated in the study and completed the well-validated NPU threat paradigm. Startle eyeblink potentiation was recorded during the task as an index of aversive responding. Participants belonged to one of two groups: a) individuals who do not currently own any handguns; and b) individuals who currently own one or more handguns. We hypothesized that individuals in the handgun ownership group would display greater reactivity to U-threat, but not P-threat, compared with the non-handgun ownership group. We also hypothesized that biological sex would moderate the group effect and that female handgun owners would display particularly enhanced reactivity to U-threat (only).

2. Methods

2.1. Participants and Procedure

Individuals were recruited from the community to participate in a study to understand risk factors for suicide among handgun owners and non-handgun owners. Specifically, we recruited digitally through Qualtrics Panels, local research registries, and social media, as well as through flyers at community events, self-defense courses, and gun ranges in the central Ohio and surrounding areas. We recruited handgun owners specifically versus firearm owners more broadly because handguns account for over 80% of firearm-related injuries and deaths in the U.S. (Planty and Truman, 2013). Long gun ownership was assessed but did not influence study eligibility. Potential participants first completed an online screening survey assessing demographic characteristics, firearm ownership, and medical conditions that could be exclusionary. Respondents whose responses suggested they were likely eligible were then contacted to schedule a virtual meeting with a member of the research team to complete an in-depth eligibility interview. Inclusion criteria were: (1) age of at least 18 years and (2) able to make one 2-hour visit to an on-campus laboratory for research-related activities. Potential participants were excluded if they had: (1) serious medical conditions that could interfere with data interpretation for laboratory procedures (e.g., deafness, moderate or severe traumatic brain injury, or lifetime mania or psychosis); (2) psychotropic medication use within the past 4 months; (3) acute alcohol intoxication (verified via breath test); and (4) heavy recreational alcohol or cannabis use, respectively defined as 5+ alcohol binges per month and cannabis use more than 5 times per week. Study procedures were approved by The Ohio State University’s Biomedical Institutional Review Board, and participants were monetarily compensated for their time.

A total of 138 individuals who enrolled in the study completed a battery of self-report questionnaires and the NPU startle task. There were 5 individuals who had unusable/poor-quality startle data and were excluded (i.e., excessive baseline artifact and/or ≥75% of blinks scored as missing or nonresponses in any one condition [Blumenthal et al., 2005]). The remaining subjects comprised the following two groups: a) individuals who currently own one or more handguns (n = 81), and b) individuals who do not currently own any handguns (n = 52). Participants were classified as handgun owners (n = 81) or non-handgun owners (n = 52) based on their responses to the following two researcher-administered interview questions administered during an eligibility interview: (1) Do you currently own a working handgun or pistol? [yes or no]; (2) How many working handguns do you personally own? [numeric value from 0-99].

2.2. NPU Threat Task

The NPU threat of electric shock task was developed to assess an individual’s responses to predictable and unpredictable threats (Schmitz and Grillon, 2012). Individuals were instructed to abstain from drugs and alcohol at least 24 hours before the laboratory assessment, which was verified via an alcohol breathalyzer and urine drug screen. Following informed consent, participants completed the NPU threat task (Gorka and Shankman, 2017; Gorka et al., 2013, 2016a, 2016b). During research-related activities for the NPU task, shock electrodes were placed on the participants’ left wrist, and a shock workup procedure was completed to identify the level of shock intensity each participant described as “highly annoying but not painful” (between 1 and 5 milliamperes [mA]). To reduce early exaggerated startle potentiation, participants completed a 2-minute startle habituation task before the task.

The NPU threat task consisted of three within-subject conditions including no shock (N), predictable shock (P), and unpredictable shock (U). Each condition lasted 145 seconds, during which a 4-second visual countdown was presented six times. In the N condition, there were no shocks delivered. During the P condition, participants only received a shock when the countdown reached 1. In the U condition, shocks were administered during any point of the countdown. Text appeared at the bottom of the computer monitor to inform participants of the current condition. The interstimulus intervals (i.e., time between countdowns) ranged from 15 to 21 seconds, during which only the text describing the condition was on the screen. There was always a minimum of 10 seconds between two probes or a shock and a probe. Startle probes were administered during both the CD and ISI during each condition. Each condition was presented two times in a randomized order (counterbalanced). Participants received 24 total shocks (12 in P and 12 in U) and 60 total startle probes (20 in N, 20 in P, and 20 in U).

2.3. Startle Data Collection and Processing

Startle data were acquired using BioSemi Active Two system (BioSemi, Amsterdam, the Netherlands), and stimuli were administered using Presentation (Albany, CA). Electric shocks lasted 400 milliseconds, and acoustic startle probes were 40 milliseconds in duration, white noise bursts of 103-decibels (dB) with near-instantaneous rise time presented binaurally through headphones.

Startle responses were recorded from two 4-mm Silver/Silver Chloride (Ag/AgCl) electrodes placed over the orbicularis oculi muscle below the left eye. The ground electrode was located at the frontal pole (Fpz) of an electroencephalography cap that the participants were wearing as part of the larger study. One startle electrode was placed 1 cm below the pupil, and the other was placed 1 cm lateral of that electrode. Data were collected using a bandpass filter of DC 500 Hertz (Hz) at a sampling rate of 2000 Hz.

Published guidelines by Blumenthal et al. (2005) were followed when processing and scoring eye blinks. Peak amplitude was defined within 20 to 150 milliseconds after the probe onset relative to baseline (i.e., average activity for the 50 milliseconds preceding probe onset). Software initially identified each peak, and data were further examined by hand to ensure acceptability. Blink magnitude values (i.e., condition averages include values of 0 for nonresponses) were used in all analyses. Blinks were scored as nonresponses if activity during the post stimulus time frame did not produce a peak that was visually differentiated from baseline. Blinks were scored as missing if the baseline period was contaminated with noise and movement artifact or if a spontaneous or voluntary blink began before minimal onset latency (Gorka, 2020). With respect to the internal consistency of the startle data, as expected, odd-even trials were significantly correlated within each condition: No-threat r = 0.94, p < .001; P-threat r = 0.95, p < .001; U-threat r = 0.91, p < .001. To account for baseline individual differences in startle magnitude we created P- and U-threat startle potentiation scores. For P-threat we subtracted startle magnitude during NCD from PCD. For U-threat we subtracted startle magnitude during NCD from UCD. Odd-even trials for the U-threat and P-threat difference scores were moderately correlated: U-threat r = 0.58, p < .001; P-threat r = 0.50, p < .001.The startle potentiation scores were then used as the primary dependent variables in subsequent analyses.

2.4. Data Analysis Plan

SPSS statistical software version 28 (2021; IBM Corp.) was used for all analyses. We first tested whether the two groups differed on any important demographic variables which could influence startle potentiation using a series of planned analyses of variance (ANOVAs) and chi-square tests. We specifically examined whether the groups differed on age, sex, race, and ethnicity. To test our hypotheses, we conducted a repeated measures analysis of variance (ANOVA) with startle potentiation to threat as a 2-level (U-threat vs. P-threat) within-subjects factor. Biological sex (female vs. male) and Group (handgun owners vs. non-handgun owners) were included as between-subjects factors. A post-hoc sensitivity analysis was conducted using G*Power (Faul et al., 2009). With a sample size of 133, power 1-β = 0.80, and α = 0.05, the study was powered to detect a small-to-medium effect size of f=0.16.

3. Results

3.1. Descriptives

Descriptive information for participants is presented in Table 1. The two groups did not differ on age, ethnicity, race, and biological sex. More specifically, there were 23 males and 29 females in the non-handgun ownership group, and 49 males and 32 females in the handgun ownership group. 58% of handgun owners reported that they regularly carry their handgun outside of the home. Handguns and pistols were the most prevalent reported gun type owned, with individuals owning 3.6 ± 4.3 on average. On average, males reported owning more handguns and pistols (F[1, 132] = 3.87, p = 0.049), shotguns (F[1, 132] = 5.20, p = 0.024), and rifles (F[1, 132] = 5.89, p = 0.017) than females.

Table 1.

Sample Characteristics

Variable	Non-Handgun Owner (n = 52)	Handgun Owner (n = 81)	X 2	F	p
Age (years)	36.2 (14.9)	35.9 (11.8)	--	0.02	.880
Sex (% female)	55.8%	39.5%	3.37	--	.066
Ethnicity (% Hispanic)	11.5%	11.1%	<0.01	--	.969
Race (%)
White	75%	77.8%	0.137		.712
Black	9.6%	12.3%	0.24		.627
Asian	9.6%	4.9%	1.10		.295
Biracial, Other or Unknown	5.8%	4.9%	0.04		.834
Carry Handgun Outside Home (%)	--	58.0%	--	--	--
No. of Firearms in Home, by Type, M (SD)
Handguns and Pistols	0.0 (0.0)	3.6 (4.3)	33.24	--	<.001
Rifles	0.2 (0.5)	1.8 (3.4)	10.56	--	.001
Shotguns	0.2 (0.6)	1.1 (1.5)	16.02	--	<.001

3.2. Differences in Startle Eyeblink Potentiation

Results of the repeated measures ANOVA are presented in Table 2. There was no 2-way group x threat condition interaction on startle potentiation. There was a main effect of threat condition such that startle potentiation was greater during U-threat relative to P-threat. There was also a main effect of sex. Females displayed greater startle to threat compared with males. These main effects were qualified by a significant 3-way group x threat condition x sex interaction.

Table 2.

Repeated Measures ANOVA examining Startle to U-threat and P-threat

Variable	df	F	p	Partial Eta Squared
Threat	1, 129	18.11	<.001	.123
Sex*	1, 129	3.98	.048	.032
Group	1, 129	1.13	.290	.009
Threat x Group	1, 129	2.65	.106	.020
Threat x Sex	1, 129	0.84	.363	.006
Group x Sex	1, 129	2.87	.093	.022
Threat x Group x Sex*	1, 129	3.99	.048	.032

Note.

^*p < .05;

Group = handgun owners vs. non-handgun owners; Threat = predictable threat vs. unpredictable threat.

To follow up the 3-way interaction, we tested the sex by group interaction at each level of threat condition (U and P). Specifically, we ran two hierarchical linear regression analyses. The main effects of sex and group were entered in Step 1. The sex by group interaction term was entered in Step 2. For the U-threat model, there were no main effects of sex (β = 0.06, t = 0.64, p = .522) or group (β = 0.06, t = 0.64, p = .522); however, there was a sex by group interaction (β = −0.59, t = −2.08, p = .040). Within females, there was no effect of group (β = −0.10, t = −0.76, p = .450). Within males, there was a significant effect of group (β = 0.28, t = 2.20, p = .030) such that male handgun owners exhibited increased startle potentiation to U-threat relative to male non-handgun owners (see Fig. 1).

Figure 1.

Bar graph displaying mean startle potentiation (μV) during predictable threat (A) and unpredictable threat (B) by handgun ownership group and biological sex. Bars reflect standard error.

For the P-threat model, there was a main effect of sex (β = 0.23, t = 2.62, p = .010); females exhibited greater startle potentiation during P-threat compared with males. There was no main effect of group (β = 0.02, t = 0.18, p = .859), or sex by group interaction (β = 0.04, t = 0.14, p = .885).

4. Discussion

Research suggests that firearm owners may be vulnerable to higher threat expectancies given uncertainty and experience chronic hypervigilance; however, this hypothesis has never been tested using an objective laboratory paradigm. The current study sought to expand existing research by examining the influence of handgun ownership on reactivity to U- and P-threat. We did not find support for a 2-way group x threat condition interaction on startle potentiation. However, we found a significant 3-way interaction with biological sex. Among males, handgun owners displayed increased reactivity to U-threat compared with non-handgun owners. However, there were no group differences in reactivity to P-threat among males. Among females, there were no group differences in startle potentiation during U-threat or P-threat. Thus, group differences were only observed during U-threat for males.

This selectively exaggerated reactivity to U-threat observed in males is noteworthy given the limited research on sex differences in threat responding in the context of firearm ownership. As described previously, the P-threat condition elicits a discrete fear response to a known threat, whereas the U-threat condition measures an individual’s level of sustained hypervigilance and anticipatory anxiety. Therefore, our data support the notion that, for males in particular, firearm possession is associated with heightened threat expectancies to uncertain stressors. This finding was somewhat surprising given previous research showing no sex differences in the likelihood of owning a handgun for protection motives (Wolfson et al., 2020), which is associated with perceptions of the world as a dangerous place (Stroebe et al., 2017) and presumably heightened threat sensitivity. In fact, females are more likely to own a firearm solely for protection (Warner, 2020). Previous studies, however, have not directly linked motives of firearm ownership with psychophysiological measures of fear or anxiety, suggesting factors beyond ownership motives contribute to threat sensitivity differences, and further research is needed.

Our results indicated no group differences in threat reactivity for females. However, there was a main effect of biological sex such that females displayed higher U- and P-threat reactivity than males across groups. This finding is consistent with previous research demonstrating increased startle reactivity, as well as threat-elicited neural activity, in females relative to males (Burani and Nelson, 2020; Dark et al., 2022; Ordaz and Luna, 2012; Stevens and Hamann, 2012). Stated another way, regardless of gun ownership status, females exhibit exaggerated sensitivity to U-threat, which has been posited to contribute to increased prevalence rates of anxiety disorders in females (e.g., Burani and Nelson, 2020). Interestingly, females report feeling more empowered by owning guns than males (Kelley, 2022) though feelings of empowerment may not necessarily translate into detectable decreases (or increases) in threat reactivity. Given that all females are more prone to heightened anxiety and threat reactivity, there may be a ceiling effect and/or gun ownership may not be a robust differentiator of startle potentiation to threat.

Together, we believe these data indicate that male handgun owners (and females, broadly) represent a unique subgroup that is characterized by increased sensitivity to uncertain stressors. Increased startle reactivity to U-threat has been associated with risk for anxiety and substance use disorders (Gorka et al., 2013) and longitudinally predicts functional impairment in individuals independent of diagnoses (Stevens et al., 2019). Reactivity to U-threat, as such, may be considered an objective, brain-based indicator of risk for adverse mental and/or physical outcomes. Future research is needed to further explore the causal links between sensitivity to U-threat, motivation to purchase or obtain a firearm, and subsequent behavior and symptoms.

If sensitivity to U-threat proves to be a key mechanism, intervening on this target may have significant public health benefit. It is important to highlight that the firearm industry has drastically shifted focus in recent decades from advertising themes of hunting and sport shooting to self-defense and concealed carry (Yamane et al., 2020). These tactics have been effective, with the percentage of Americans who believe that having a firearm in their home would make them safer rising from 35% in 2000 to 63% in 2014, despite clear evidence indicating otherwise (McCarthy, 2014). These threat- and protection-focused messages may increase anticipatory anxiety, particularly in individuals who are already vulnerable and sensitive to uncertain threats, and motivate firearm ownership as a coping mechanism. If these processes are perpetuating ownership, scalable and accessible strategies aimed at reducing sensitivity to uncertain stress would be beneficial. For instance, semi-structured counseling programs that have been developed to facilitate discussions between physicians and patients regarding the risks of firearm ownership could be adapted to include elements of tolerating and responding to uncertainty to disrupt the negative reinforcement cycle perpetuating ownership (Weinberger et al., 2015).

Strategies to reduce U-threat reactivity may prove beneficial not only for alleviating factors that may motivate firearm acquisition and possession but also for reducing firearm-related suicide risk. Evidence for a role of threat sensitivity in suicidality comes from research demonstrating a connection between negative emotional tendencies with suicidal tendencies and clinical conditions associated with suicide (e.g., depressive and anxiety-related disorders; Brandes and Bienvenu, 2006; Khan et al., 2005). Additionally, high threat sensitivity has been shown to uniquely predict suicide risk beyond internalizing and externalizing problems (Venables et al., 2015). Relatedly, history of suicidal ideation has been shown to be associated with increased startle reactivity to U-threat, but not P-threat, during the NPU paradigm (Lieberman et al., 2020). Given the current findings and existing research demonstrating a clear link between firearm ownership, as well as owning a firearm for self-protection reasons, and increased risk of suicide (Goldberg et al., 2019; Miller et al., 2013), U-threat sensitivity is likely a key component in determining and diminishing risk for suicide among male handgun owners in particular.

The current study had several strengths. Participants were medically and physically healthy, medication free, and tested negative for alcohol and drug use the day of the assessment. We used a well-validated threat task and an objective, brain-based index of aversive reactivity. There were also several limitations. First, because of the study’s sample size, we were unable to split the handgun group into smaller subgroups based on, for example, number of handguns owned. Second, motivational reasons for firearm acquisition and ownership were not assessed. While previous research has shown that most individuals own handguns for self-protection, with minimal differences between sexes (e.g., Wolfson et al., 2020), motivational differences in firearm ownership were unaccounted for and may have impacted findings from the current study. Third, the cross-sectional design restricted our ability to assess directional effects among variables of interest. Therefore, we could not determine if handgun owners’ threat reactivity increased or decreased following the acquisition of their handguns. Future research focused on these sequential occurrences could provide more nuanced information about how handgun ownership affects threat reactivity.

In summary, the results indicate that biological sex impacts the association between handgun ownership and startle reactivity to threat. While male handgun owners showed exaggerated U-threat reactivity compared to non-handgun owning males, there were no differences in threat responding for females across the two groups. Moreover, females overall had increased threat reactivity compared to males. Ultimately, our findings provide novel information about the impact of handgun ownership on threat sensitivity and highlight the need to consider both biological sex and threat type when examining these associations. The findings implicate new lines of research focused on targeting individual differences in neurobiologically based processes such as threat sensitivity when considering the role of handgun ownership in treatment strategies to prevent firearm injury and mortality.

Highlights.

• Firearm owners are vulnerable to anxiety though biological sex likely plays a role

• We examined the impact of handgun ownership and sex on objective threat reactivity

• Male handgun owners exhibited increased startle reactivity to unpredictable threat

• There was no impact of handgun ownership on startle reactivity to threat in females