What the split between regulation and reactivity actually looks like
The clearest evidence comes from a study that measured several emotional processes in the same people. Sixty healthy adults were assigned either to stay awake all night or to sleep normally, then tested on mood, attention to emotional stimuli, emotional working memory, categorization, and emotion regulation [1]. The sleep-deprived group felt less positive overall, yet they did not rate emotional images differently from rested participants, and the emotional content of the tasks did not trip them up in attention, memory, or categorization [1].
The one place they diverged was regulation: sleep-deprived participants were less effective at regulating negative emotion [1]. That pattern is the heart of the answer. Feeling and perceiving emotional material looked intact; deliberately managing it did not.
A separate imaging study describes a related shift in the brain. Over a 39-hour period of total sleep deprivation, scans taken every six hours showed the amygdala becoming more strongly coupled with salience-network regions such as the anterior cingulate cortex and insula, while its connections with sensory, visual, and attentional areas weakened [5]. The authors interpret this as the brain leaning more on amygdala-driven threat and body-state signals as external sensory input becomes less reliable [5].
Why deliberate regulation may be the fragile part
Regulating an emotion is a controlled, effortful process: you have to notice the feeling, hold a goal in mind, and apply a strategy. The sleep-deprivation study frames its result this way, concluding that sleep loss reduced the controlled processing required for emotion regulation rather than biasing emotional processing in general [1].
The imaging findings fit that framing but add a twist. Rather than a simple loss of prefrontal braking on the amygdala, the authors describe a progressive reorganization in which emotional circuitry shifts toward salience and threat detection while top-down control weakens [5]. They present this as a possible adaptive response to degrading sensory and attentional systems, not as a settled mechanism [5].
Work on partial sleep deprivation reaches a similar conclusion about the top-down side, reporting impaired top-down regulation with bottom-up processes left unaffected [3]. That extends the pattern beyond a single night of total sleep loss, though the evidence there comes from a task using emotional arrows and includes an age-related angle [3].
Does getting more sleep help, and what is still open
If sleep loss weakens regulation, does extra sleep strengthen it? A small nap study asked participants to suppress, maintain, or enhance their emotional response to negative and neutral pictures after either a nap or an equivalent period awake [4]. Participants could shift their reported emotional valence and arousal on instruction, but the neural measure the researchers tracked did not differ significantly between the nap and wake conditions, and the sample was very small [4]. The authors read the pattern as hinting that napping may support top-down control of amygdala-driven responses, but the result is suggestive rather than demonstrated [4].
Other work links sleep loss to worsened mood and examines bottom-up experiential regulation against top-down cognitive reappraisal, but the available summary is too fragmentary to say how those two strategies fared relative to each other [2]. What the fuller picture does support is the core asymmetry: the automatic emotional response appears relatively preserved, while the controlled machinery for managing it is what suffers.
Sources used in this answer
Total sleep deprivation reduces top-down regulation of emotion without altering bottom-up affective processing
Total sleep deprivation reduced positive affect and impaired regulation of negative emotion, but did not bias ratings or task performance involving affective stimuli, indicating intact bottom-up affective processing alongside weakened top-down regulation.
Bottom-up and cognitive top-down emotion regulation: Experiential emotion regulation and cognitive reappraisal on stress relief and follow-up sleep …
The paper compares bottom-up experiential emotion regulation with top-down cognitive reappraisal and reports that sleep loss worsens mood, though the available abstract is too incomplete to detail the strategy comparison.
Functional connectivity of the cognitive emotion regulation network in partially sleep-deprived individuals using an emotional arrows task: potential age-dependent …
In partially sleep-deprived individuals performing an emotional arrows task, sleep loss impaired top-down emotion regulation while leaving bottom-up processes unaffected, with a possible age-dependent component.
0151 Modulating Emotion Regulation and the Late Positive Potential ERP Component through Sleep Extension
In a small within-subjects nap study, participants could alter emotional valence and arousal on instruction, but the late positive potential did not differ significantly between nap and wake conditions.
0225 Reconsidering the Human Emotional Brain Without Sleep: Is it a ‘Prefrontal-Amygdala Disconnect’ or Reorganization of Amygdala-Centric Networks?
Across repeated scans during 39 hours of sleep deprivation, amygdala connectivity shifted toward salience-network regions and away from sensory and attentional areas, consistent with weaker top-down control and stronger bottom-up salience processing.