The Impact of a Rosemary Containing Drink on Cognition and Mood: The Role of Eye Blink Dynamics

1. Introduction

Rosemary is a herb native to the Mediterranean region and has long been associated with cognitive enhancement and psychological wellbeing. Historically, rosemary was used in Egyptian burial rituals and symbolised fidelity and remembrance in ancient Greek ceremonies, including weddings and funerals (see [1,2]). The association with memory and cognition is not purely symbolic. In Hamlet, Ophelia remarks, "There’s rosemary, that’s for remembrance” (4.5.175), reflecting early cultural intuitions of its mnemonic effects [3]. Its presence in such traditions, alongside evidence of physical and psychological benefits, has contributed to its reputation as a cognitive enhancer [4]. Carnosic and rosmarinic acid are two of the active ingredients of rosemary, which have known antioxidant and anti-inflammatory properties. These compounds support the immune system, offer relief from pain, and are linked to cardiovascular protection [5]. Rosemary's anxiolytic and stimulatory effects have also been linked to reduced stress, improved emotional regulation, and particularly relevant here, cognitive facilitation [6]. In the present study, we aim to identify the specific mood and attentional components that improve during cognitive task engagement and examine the moderating effects of dopamine linked blink metrics.

Consider first acetylcholine (ACh), a neuromodulator central to attention and memory [7]. ACh is typically released from the basal forebrain, notably the nucleus basalis of Meynert, with widespread cholinergic projections targeting the cortex [8,9]. These projections support both synaptic and volume transmission, allowing broad modulation of cortical activity thought to be involved in attentional control, including the regions of the frontoparietal and default mode networks [10]. The active compounds of rosemary, including 1,8-cineole and carnosic acid, have been shown to inhibit acetylcholinesterase (AChE) and may increase ACh availability [11]. This finding is consistent with the action of pharmaceutical cholinesterase inhibitors used in the treatment of Alzheimer's disease [12]. Animal models also suggest rosemary may have anxiolytic and antidepressant effects alongside AChE inhibition properties [12]. These findings suggest cholinergic involvement. However, given rosemary's influence on attentional and affective processes, examining dopaminergic pathways may offer a theoretically grounded and potentially worthwhile route to examine the enhancing properties of rosemary further.

In addition to involvement in emotional processing, dopamine plays a critical role in the regulation of attention and executive function, particularly in the filtering of distractions and the processing of novelty [13]. Disruptions in dopamine signalling in the prefrontal cortex and basal ganglia may impair a variety of aspects of attention functioning and behaviour (see [14] for a review). This neurochemical framework has informed a range of pharmacological interventions. For instance, psychostimulants such as methylphenidate and amphetamines, commonly used in the treatment of ADHD, enhance dopaminergic transmission and improve attentional ability [15]. Similarly, dopaminergic agents have been explored in cognitive enhancement studies targeting episodic memory and attention in clinical populations, including Parkinson's disease [16] and schizophrenia [17]. Nutritional interventions have also demonstrated modulatory effects on dopamine. Tyrosine, a dietary precursor to dopamine, has been shown to influence cognitive performance under stress and fatigue [18]. Therefore, it is hardly surprising that compounds found in a variety of herbs, such as rosemary, may exert dopaminergic effects possibly by interacting with brain receptors. Specifically, rosemary's antidepressant-like properties have been linked to activity at dopamine D1 and D2 receptors, as well as noradrenergic and serotonergic systems [19]. These interactions suggest a broader neuromodulatory profile that may contribute to its cognitive and mood-related effects. From a neuropsychological perspective, eye blink rate (EBR) has emerged as a non-invasive proxy for central dopamine activity and is employed in the present study.

While the relationship is unclear, EBR has been shown to vary across clinical populations in ways that may reflect dopaminergic status. For example, elevated blink rates are often reported in schizophrenia, while reduced rates are typically observed in Parkinson's disease [20], which is consistent with underlying dopamine dysregulation. Our previous work on the enhancing properties of music, mind wandering, and creativity (e.g., [21]), alongside studies elsewhere [22], has established the use of blink metrics as indicators of dopaminergic function, attentional control, and emotional processing. Importantly, blink rate is sensitive to cognitive and motivational demands, and may increase during internally focused states involved in self-generated thoughts [23]; [24]. Blink variability (EBV), though less commonly discussed, may reflect transient shifts in attentional engagement but is included due to the partial exploratory nature of the present work.

The Current Study

The present study aimed to investigate the cognitive and mood-enhancing effects of rosemary ingestion, with a focus on the moderating role of eye blink metrics. Eye blinks were used as putative non-invasive proxies of dopamine function and attentional control, allowing us to explore individual differences in responsiveness to rosemary. Building on previous work linking rosemary to cholinergic mechanisms, this study examined whether dopaminergic tone influences cognitive performance and subjective mood. Reaction time data were analysed using ex-Gaussian modelling (Mu, Sigma, Tau) to provide a comprehensive examination of attentional engagement during task and mirrors previous work on Stroop task performance [25]. In addition, the P3a ERP component was included as a secondary and confirmatory index of dopaminergic activity to aid in the interpretation of the blink-related findings. While P3a is often linked to dopaminergic activity, it may also reflect broader physiological aspects of dopamine function beyond baseline activity. By integrating behavioural and electrophysiological measures, the study aimed to clarify how rosemary interacts with baseline neurocognitive states to influence attention, arousal and mood.

2. Methods

2.1. Participants

Forty-eight adults participated in the study (32 women; Mean age = 30.7; Range 18-63; SD = 11.2). All participants were right-handed and reported no history of neurological disorders. Screening excluded individuals with a current diagnosis of depression or anxiety, substance use, migraines, or any of the following: anaemia, heart disorder, high blood pressure, respiratory disorder, diabetes, pregnancy, history of seizures, or current use of prescribed, illicit, or herbal medication. Participants with food allergies or sensitivities were also excluded. Allocation to treatment condition was randomised prior to testing. Ethical approval was granted by the Department of Psychology Ethics Board at Northumbria University (Reference-882), and all procedures were conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants. Further details and a description of part one of this program of work can be found in [26].

2.2. Treatment

Participants consumed either 330ml of rosemary water or plain still water. The rosemary drink was supplied by No1 Botanicals and contained both a volatile oil extract and a hydrolat derived from fresh rosemary via steam distillation. The extract included terpenes such as 1,8-cineole (0.025 mg/ml) and rosmarinic acid (0.13 mg/ml), while the hydrolat contained lower levels of terpenes (1,8-cineole at 0.012 mg/ml) and no rosmarinic acid. Production and analysis were carried out by Blue Sky Botanics, Castle Farm, Upton Bishop, Ross-on-Wye, UK.

To maintain blinding, participants were informed that both drinks had been matched for taste. Those in the rosemary condition were told the placebo had been flavoured to match, while those in the control condition were told the rosemary extract had been taste-neutralised. The researcher was also blind to condition allocation.

3. Measures

3.1. The 3-Stimulus Odd-Ball Task

Participants completed a 3-stimulus visual odd-ball task designed to assess attentional control [27]. Stimuli were presented using E-Prime software on a 17.5-inch monitor. The task involved discriminating between three types of stimuli: a frequent standard stimulus (green square, area = 16 cm²; 74% of trials), a rare target stimulus (red circle, area = 12.6 cm²; 13% of trials), and a novel distractor stimulus (green square, area = 256 cm²; 13% of trials). Each stimulus was displayed for 100 ms, followed by a variable interstimulus interval between 830 and 930 ms. Participants responded to target stimuli using the spacebar on a PC keyboard. A short practice block preceded the main task to ensure participants understood the nature of the task.

3.2. Electrooculograms (Eye Blinks)

Vertical electrooculograms (VEOG) were recorded using electrodes placed above and below the eye to capture blink activity. Participants were asked to minimise excessive blinking and movement during the task. Researchers responsible for blink identification were trained in the characteristics of ocular EEG data, including blink duration, waveform shape and tempo. Eye blink rate (EBR) was calculated as the total number of blinks occurring during the 8-minute odd-ball task. Eye blink variability (EBV) was assessed by dividing the task into eight 60-second intervals and calculating the standard deviation of blink counts across these intervals.

3.3. Event-Related Potentials

Although ERP data were recorded during the task, only the P3a (measured at the Cz scalp electrode) was used as a secondary dopamine metric, as the current paper focuses on blink metrics, subjective arousal and cognition. A Biosemi electrode cap (biosemi.com) with 32 channels of EEG recordings were employed to measure ERP's. Signals were digitised at a rate of 2048Hz, with a recording epoch of 1200ms. Full details of the methodology can be found in [26], where the neuroimaging aspects of this program of work are described.

3.4. Mood and Arousal Measures

Subjective mood and arousal were assessed using the Bond–Lader visual analogue scales. This measure comprises a series of bipolar items presented as 100 mm horizontal lines anchored by opposing adjectives (e.g. "alert–drowsy", "calm–excited", "contented–discontented"). Participants were asked to mark a point along each line that best represented their current state. Ratings were collected immediately before and after completion of the odd-ball task. Scoring involved the grouping into three composite dimensions: alertness, calmness, and contentedness. These composites were derived by averaging relevant items within each dimension, as outlined in the original Bond–Lader methodology [28]. The resulting scores were used to examine changes in subjective state across the testing session and to evaluate potential treatment effects.

4. Results

4.1. Subjective Arousal and Mood Ratings

Participants completed ratings of alertness, calmness, and contentedness before treatment and after the task. Paired-samples t-tests (1-tailed) were conducted to assess pre–post changes. In the rosemary condition, there was a significant increase in alertness from pre- to post-task (t(22) = –2.41, p = .013). Participants also reported feeling significantly more content after the task compared to baseline (t(22) = –2.63, p = .008). There was no significant change in calmness. In the control condition, no significant changes were observed for alertness or calmness. However, there was a significant increase in contentedness, with scores rising from pre- to post-task (t(22) = –1.97, p = .031). Overall, these results indicate that rosemary significantly enhanced subjective alertness and contentedness, while the control condition only showed a modest improvement in contentedness, likely due to task completion effects. Treatment effects are summarised in Table 1.

4.2. Blink Metrics (Total Rate and Variability)

An ANCOVA was conducted to examine whether the effect of condition (rosemary vs control) on mean response time μ was moderated by individual differences in EBR. The overall model was significant, F(3, 38) = 3.08, p = .039, partial η² = .20. There was a trend-level main effect of condition, F(1, 38) = 3.52, p = .068, partial η² = .09. The interaction between condition and blink rate was significant, F(1, 38) = 8.08, p = .007, partial η² = .18, indicating that the relationship between blink rate and mu differed depending on condition. Specifically, higher blink rates were associated with faster responses in the control group, but slower responses in the rosemary group, reflecting a reversal in slope across conditions (see Figure 1).

An ANCOVA was conducted to examine the effect of aroma drink condition (control vs. rosemary) on response time variability (σ), with EBR entered as a continuous between-subjects factor. The interaction between condition and blink rate was significant, F(1, 38) = 4.69, p = .037, η² = .110, indicating that the relationship between blink rate and σ differed by condition (see Figure 2), with the association restricted to rosemary.

A further ANCOVA revealed that the main effects of condition and blink rate, as well as their interaction, were not significant, indicating no meaningful differences in τ (reflecting lapses of attention; [24]) across conditions or as a function of blink rate. Similarly, an ANCOVA examining the proportion of hits revealed no significant main effect of treatment, nor a significant interaction with blink rate.

To explore whether P3a amplitude (measured at Cz scalp electrode) was associated with blink rate, an ANCOVA was conducted. The main effect of condition approached significance, F(1,34) = 3.77, p=.061, η² =.10, with higher P3a amplitudes in the rosemary condition.

The next series of ANCOVAs considered EBV. When considering mu, there were no significant main effects or interaction effects observed for mean response time μ when including blink variability in the model. An ANCOVA revealed a significant main effect of condition on σ, F(1, 38) = 4.92, p = .033, η² = .115, with greater response variability in the rosemary condition than control. Importantly, a significant interaction between condition and blink variability emerged, F(1, 38) = 4.83, p = .013, η² = .203, indicating that the effect of the drink on σ depended on individual differences in blink variability (see Figure 3).

An ANCOVA examining τ revealed no significant main effect of condition, nor a significant interaction with blink variability. Similarly, the ANCOVA examining hit rates and the P3a amplitude both revealed no significant main effect of condition, nor a significant interaction with blink variability.

4.3. Bivariate Correlations

Pearson's bivariate correlations were computed to assess the relationships between all variables, as shown in Table 2 and Table 3.

5. Conclusions

This study demonstrates that rosemary’s cognitive and mood-enhancing effects are state-dependent, varying systematically with individual blink profiles that index dopaminergic tone and attentional control. Theoretically, this extends existing cholinergic accounts by introducing a dual-neuromodulator framework in which rosemary influences both acetylcholine- and dopamine-related mechanisms of attention and arousal. The integration of blink dynamics, ex-Gaussian modelling, and electrophysiological measures offers a novel and reproducible approach for examining how botanical interventions interact with baseline neurocognitive state in cognitive enhancement.