How soon will your competent? doctor get you an objective testing protocol on this to verify your indoor environment is OK?
Do you prefer your doctor, hospital and board of director's incompetence NOT KNOWING? OR NOT DOING? Your choice; let them be incompetent or demand action!
Indoor Environmental Quality and the Brain: A Systematic Review of Physiological and Neural Evidence
Under a Creative Commons license
Open access
Keywords
Indoor environmental quality (IEQ)
Neuroarchitecture
Brain
Body
Thermal Comfort
lighting
Productivity
1. Introduction
Individuals are estimated to spend approximately 80-90% of their time indoors [1], primarily within environments such as homes, offices, and educational institutions, settings that not only shape daily experiences but also influence a wide range of physiological and brain responses [2],[3]. In this context, neuroarchitecture has emerged as an interdisciplinary field at the intersection of neuroscience, environmental psychology, and architecture [4], seeking to understand how the built environment is perceived, processed, and represented in neural activity and brain processes [5]. From this perspective, insights from neuroscience can deepen our knowledge of how spatial environments are perceived and cognitively processed, thereby informing architectural decision-making, guiding design strategies grounded in empirical evidence, and supporting policies aimed at enhancing human health and well-being [6],[7]. Therefore, it is worth investigating the relationship between indoor environment quality (IEQ) and human responses. Understanding this relationship requires examining how the human body and brain interact with the indoor environment at both sensory and neurophysiological levels. Environmental stimuli, such as temperature, lighting, air quality, and noise, are detected by sensory receptors and transmitted through peripheral neural pathways to the central nervous system, where they are integrated and interpreted by the brain, forming our perception of the environment [8]. Given this close interplay, the quality of the indoor environment has become a critical determinant of human functions [9].
Investigating IEQ is complicated due to the interplay of multiple factors that affect occupants both physically and psychologically. Previous studies classify IEQ into five key categories: thermal conditions, indoor air quality (IAQ), acoustics, lighting [10],[11], and non-light visual elements, such as biophilic design and access to views [12],[13]. Evidence consistently demonstrates that poor IEQ conditions can significantly affect comfort, health, well-being, and productivity, with each factor affecting these outcomes independently [14],[15]. A growing body of evidence highlights that environmental stressors, such as extreme thermal conditions [16],[17],[18],[19], inadequate ventilation [20], poor air quality [21],[22],[18], inappropriate lighting [23],[24],[25],[26], and excessive noise [27],[28],[29], can impair cognitive performance and disturb physiological functions [30]. However, most studies tend to examine these effects separately, overlooking the complex interdependencies among them [10],[12].
2. Categories of IEQ factors and their effects
This review synthesizes the existing literature by categorizing indoor environmental quality (IEQ) into five primary dimensions: thermal conditions, lighting, non-light visual elements (e.g., views and biophilic design), indoor air quality (IAQ), and acoustics. These dimensions are examined in relation to four main human outcome domains commonly explored in the literature: comfort, well-being and health, productivity, and emotion. This section provides an overview of each IEQ factor and its relevance to occupants’ responses, with a particular emphasis on neurophysiological mechanisms.
2.1. Indoor environmental quality
2.1.1. Thermal environment
The thermal environment refers to the physical conditions that govern heat exchange within indoor spaces. It influences individuals thermal perception and, consequently, their overall thermal comfort [13]. Thermal comfort, as a key component of IEQ, has a direct influence on human physiology and brain function [31]. According to ASHRAE (2017), thermal comfort is defined as a mental state that indicates an individual's satisfaction with the ambient thermal environment. This condition is mainly determined by four physical parameters, such as air temperature, mean radiant temperature, air velocity, and humidity. In addition, personal characteristics, including clothing insulation, metabolic rate [32], gender [33], age [34], cultural background [35], and physiological adaptation [36], interact with environmental variables to shape overall thermal comfort.
From a neurophysiological perspective, thermal stimuli activate thermoregulatory processes through the hypothalamus, particularly the preoptic area (POA), which integrates input from skin and core thermoreceptors. This integration triggers autonomic physiological responses, such as heart rate changes, vasodilation or vasoconstriction, and sweating to maintain thermal homeostasis [37],[38]. Beyond physiological regulation, thermal stress influences brain function and cognitive performance by altering hormone levels (e.g., cortisol), mood, and mental capacities such as attention, working memory, and decision-making [16],[39]. Studies report that exposure to temperatures above 30°C leads to reduced concentration and slower reaction times in both students and office workers [40]. These findings underscore the importance of thermal comfort in maintaining both cognitive efficiency and physiological stability.
2.1.2. Lighting
Lighting is a key dimension of IEQ that influences not only visibility and cognitive functions, but also circadian rhythms, neuroendocrine activity, and mood. While artificial lighting meets functional needs, natural daylight, due to its spectral composition, stimulates various biological processes and supports psychological comfort, circadian alignment, and sleep regulation [41],[42],[43]. Light quality for visual comfort is defined by photometric parameters, including luminance, illuminance, glare, and correlated color temperature (CCT), which also influence neurological responses [13]. Studies have reported increased theta activity in the right fronto-temporal and left temporo-parietal areas under subjectively pleasant lighting conditions, suggesting altered neural states related to affective processing [44]. Optimized lighting, considering spectrum, intensity, timing, and duration, has been shown to improve mental clarity, working memory, and task engagement [45],[42],[43],[19]. For instance, high illuminance and cool light (6500 K) reduce EEG alpha power and enhance alertness and reaction times in office-like environments [46].
By integrating chronobiological and neuroscientific principles into architectural lighting design, such as through optimized orientation, atriums, and dynamic façades, built environments can simultaneously support circadian rhythm, health, cognitive performance, and occupant satisfaction [47],[12]. For example, recent evidence suggests that adaptive facade systems, which dynamically modulate daylight and shadow patterns, have been shown to elicit positive emotional responses and enrich occupants’ sensory experiences. Such adaptive systems contribute not only to visual and thermal comfort but also to affective well-being by enriching the sensory and emotional engagement with architectural space [48]. Beyond these visual and performance-related effects, light exposure can enhance occupants' alertness and performance through a "non-visual" photoreception system, which relies on melanopsin-expressing retinal ganglion cells (mRGCs), thereby directly linking lighting conditions to neurophysiological states. In other words, this non-visual pathway improves brain function and alertness even in the absence of light for vision [49].
2.1.3. Non-Light visual factors
In addition to lighting, non-light visual attributes, such as spatial geometry, surface textures, color schemes, and outdoor views, play a crucial role in shaping perception, mood, attention, and cognitive performance. For instance, research suggests that cooler hues like blue and green are often linked with calmness and creativity, while warmer tones such as red may improve alertness and attention to detail [50],[51]. Similarly, environments offering moderate visual complexity, featuring varied textures, layered arrangements, or changing wall art, can stimulate intellectual curiosity and restore attention in line with Attention Restoration Theory (ART) [52]. Beyond artificial elements, natural visual features, as emphasized by the biophilia hypothesis, enhance well-being and performance. The findings have generally confirmed that exposure to greenery and outdoor landscapes triggers higher alpha rhythms recorded by EEG in the frontal lobes [53],[54]. Similarly, fMRI and NIRS findings indicate reduced frontal lobe activation during exposure to natural scenes [55],[56],[57], which are associated with lower stress and greater relaxation [58],[59],[60]. Collectively, balanced visual environments that combine appropriate color use, moderate complexity, and visual coherence can support both emotional stability and cognitive efficiency in indoor spaces.
2.1.4. Indoor air quality
IAQ focuses on minimizing indoor pollutants such as CO₂, volatile organic compounds (VOCs), and particulate matter (PM), which have been shown to impair neural activity and cognitive functions, including attention, memory, decision-making, and sensory or emotional processing [20],[13],[61],[62]. Practically, exposure to elevated CO₂ levels (up to 3000 ppm) and bioeffluents has been associated with physiological stress markers, such as increased salivary α-amylase and elevated blood pressure. At the same time, heart rate exhibits a smaller decrease compared to baseline conditions [63]. Gao et al. (2022) further demonstrated that exposure to elevated levels of VOCs emitted from interior paint significantly altered EEG patterns, specifically decreasing alpha power and increasing theta activity, indicating reduced attentional focus and increased mental fatigue [64].
2.1.5. Acoustic
Indoor noise stems from both internal and external sources, including occupant activities [65] and outdoor environmental sounds [66]. Common internal contributors include conversations, HVAC operations, and office equipment [67],[68], while external noise may originate from traffic or construction, often intruding through building envelopes. Unwanted noise in indoor spaces is widely recognized as a stressor that disrupts cognitive functioning, emotional regulation, and overall well-being. Exposure to high or fluctuating noise levels has been shown to impair attention, working memory, and task performance, particularly in learning and working environments [69]. For example, classroom noise above 40–50 dB(A) has been associated with reduced reading comprehension and lower standardized test scores in children [70].
2.2. Effects of indoor environmental factors
IEQ encompasses multiple, interacting physical attributes of built spaces that shape human experience. Previous research indicates that these indoor environmental dimensions exert multidimensional effects on human functioning, including occupants' comfort and well-being, health, as well as cognitive performance and productivity [71],[12],[13].
Productivity is one of the most extensively examined outcomes of IEQ factors. It reflects the brain’s capacity to sustain attention, process information efficiently, and execute goal-directed tasks through coordinated activity within the prefrontal and parietal cortices. Specifically, the dorsolateral and ventrolateral prefrontal cortices support executive control, working memory, and task planning [72],[73], while the medial and orbitofrontal regions of the prefrontal cortex contribute to motivation and decision-making, and reward evaluation [74]. The parietal cortex, in turn, supports attentional allocation and spatial working memory, in coordination with prefrontal regions [75]. A growing body of research demonstrates that exposure to high-quality environments minimizes distractions and stressors, supporting attention, memory, and problem-solving by regulating factors such as core temperature, circadian rhythms, and hormone levels [76],[12].
Further, multiple studies demonstrate that perceptions of indoor environmental quality are strongly linked with occupants’ comfort. Occupants’ comfort refers to the state in which individuals experience well-being and satisfaction, encompassing both the surrounding environment and its perception by the human body [77]. Experiencing comfort engages interconnected regions within the limbic and prefrontal networks, notably the insula, anterior cingulate cortex (ACC), amygdala, and orbitofrontal cortex, areas responsible for emotional regulation, interoception, and reward processing. When individuals perceive their surroundings as comfortable, activity within stress-related circuits decreases, such as the insula and amygdala regions. At the same time, areas involved in positive affect and sensory integration, including the orbitofrontal and prefrontal cortices, become more active, leading to reduced physiological arousal and enhanced cognitive efficiency [78],[79]. Thus, comfort is not merely a subjective feeling, but a neurobiologically grounded state that reflects harmony between environmental inputs, bodily sensations, and brain regulation mechanisms. Figure 1 summarizes the brain regions most frequently associated with comfort and productivity.
Fig. 1While comfort represents an immediate and perceptual response, prolonged exposure to suboptimal indoor conditions can lead to physiological strain and the development of health-related symptoms, including fatigue, headaches, and stress, which can affect individual well-being [80]. The relationship between indoor environments and mental health has been extensively studied, with findings suggesting that high-quality indoor environments reduce fatigue, anxiety, and irritability, often caused by poor lighting, noise, or thermal discomfort [81]. Growing evidence indicates that mental and physical health are interconnected through shared neural systems that regulate both somatic physiology and higher-order cognition. These regions often interact within large-scale brain systems, including the default mode network (DMN) and prefrontal cortical circuits. The default mode network primarily involves the medial prefrontal cortex, posterior cingulate cortex/precuneus, angular gyrus, and medial temporal regions, supporting self-referential processing, autobiographical memory, and the integration of experience across time [82]. Most psychiatric disorders are not the result of localized dysfunction in isolated regions of the brain. Rather, they arise from problems in how multiple brain regions communicate and interact with each other.
The relationship between the environment and human responses is inherently complex. While most reviews specifically focus on environmental features, understanding the broader context of how different indoor environments interact with physiological and neural systems is crucial. Research in this area has evolved considerably in recent years, shifting from traditional approaches based on questionnaires and self-reported surveys to the incorporation of neuroscientific methods within architectural research, known as neuroarchitecture, which objectively measures human responses, perceptions, and emotional reactions to spaces. These advances indicate that IEQ factors not only shape conscious experience but also modulate autonomic nervous system activity and brain function, as shown by EEG variations under different environmental conditions [83],[84],[85]. Collectively, these insights suggest that human responses to environmental changes are not passive; rather, the body actively engages in an integrated set of physiological, psychological, cognitive, and behavioral processes. Such developments provide architects and environmental researchers with deeper insights into how environmental features shape perception, emotion, cognition, and behavior. Figure 2 provides an overview of key IEQ factors and their impacts on humans.
Fig. 23. Methods
Systematic literature reviews ensure a transparent, structured, and comprehensive understanding of a research topic [86],[87],[88]. To systematically identify how IEQ influences human brain and body responses, we conducted a thorough search of the relevant scientific literature using two complementary approaches, a conventional manual review and a keyword co-occurrence analysis. The conventional manual review concentrated on the most relevant studies regarding the clear correlation between IEQ factors and brain and body responses. The methodology applied in this systematic review followed the principles outlined in the Cochrane Handbook [89]. In addition, a transparent protocol guided by the PRISMA framework (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) was employed [90]. Although many studies refer to IEQ and its bodily or neural effects, most address these aspects only indirectly, without explicitly examining the relationship. Nevertheless, these studies contain valuable information that can enhance our understanding of how IEQ factors relate to body or brain responses. By applying keyword co-occurrence analysis, this review uncovers patterns and insights from these studies that might otherwise remain hidden.
More at link.
No comments:
Post a Comment