Reactivity Is Not Aggression: The Neuroscience of the Lunging Dog

1. What "Reactivity" Means, and What It Does Not

1.1 It Is Not a Scientific Category

"Reactivity" is a practitioner term. It has no standard operational definition in the peer-reviewed literature, no validated measurement instrument, and no established prevalence figure. Compare aggression, which research defines operationally as barking, lunging, growling or biting precisely so that different studies count the same thing (Casey et al., 2014). Nothing equivalent exists for reactivity.

This is not a reason to stop using the word. It is a reason to notice what it does: it describes the handler's experience — a sudden, intense, hard-to-interrupt response to a trigger — without specifying the dog's motivation, the emotional state behind it, or the function the behavior serves.

1.2 What the Word Bundles Together

At least four different situations get the same label. A fearful dog creating distance. A frustrated dog whose approach is blocked. A dog whose arousal is already high before the trigger appears. And a dog in pain whose threshold for any response has dropped (as chronic pain does).

These share a topography and little else. Grouping them by appearance is how a single training plan comes to be applied to problems with opposite drivers.

1.3 Why the Distinction Changes the Plan

Increasing distance addresses the fearful dog's problem directly. For the frustrated dog it can lower arousal but does not, on its own, resolve the core problem. Waiting for calm before allowing approach addresses frustration and misses the point for fear. Getting this wrong is not a minor inefficiency — it means running an intervention whose mechanism does not apply to the case in front of you.

1.4 Why a Non-Scientific Word Still Earns a Place

Reactivity is not a diagnostic category, and it names something households recognize immediately. That is worth something: a term that gets people to describe the problem is more useful than a precise one nobody uses.

The cost is that the word groups cases with different causes and different treatments, which is why this article spends its length pulling them apart rather than defending or rejecting the term. Arguing about the word is less useful than asking which case is in front of you.

2. How Reactivity Is Assessed

2.1 There Is No Instrument

No validated canine measure of reactivity exists, because the term is not a scientific category. What exists is assessment of the components: fear, frustration, arousal, inhibitory control and aggression each have partial measures, and reactivity is a household word covering combinations of them. Anyone claiming to have measured a dog's reactivity has measured something narrower and called it that.

2.2 What an Assessment Actually Records

Distance at which the dog first orients, distance at which it stops being able to take food, what the display consists of, how long it lasts, and how long recovery takes. Five observations, all countable, none requiring interpretation. The last two matter most and are collected least often, because a household watching a reactive episode is not usually timing anything.

Those five answer more practical questions than any label, and they can be compared across weeks in a way a label cannot. Recording them at the start also prevents the conclusion after a month that nothing has changed, which is the point at which most households stop.

2.3 Why Video Helps and Does Not Suffice

Footage settles what the dog did and preserves the sequence, which is what distinguishes a lunge that began with a freeze from one that began with a forward orientation. What it cannot supply is the history, the medical status and the household context, which is where the differential is decided. Footage of the episode plus a history is a reasonable basis; footage alone is not.

A video plus three questions is a reasonable assessment. A video alone is one channel at one moment, and it is also usually the worst moment, since that is what prompted the recording.

2.4 The Questions That Separate the Routes

Whether the behavior occurs off leash, whether it occurs when the dog can leave, whether it stops when the target disappears or continues afterwards, and what happens if distance is increased. Each has a different answer under the fear and frustration accounts, and asking all four takes less time than watching one episode.

A dog that settles as soon as the other dog is out of sight is not the same case as one that keeps scanning for ten minutes, and the difference is visible without any equipment.

2.5 Rule Out the Body First

A dog that has become less tolerant of approach, of handling or of other dogs over weeks is a candidate for a medical workup before any behavioral account is accepted. Pain lowers the threshold and produces exactly the presentation this article describes.

That is a single sentence in a first consultation and it changes what happens next more often than any technique. Orthopedic and dental pain are the common findings, and neither is visible on a walk. A dog that is otherwise moving normally can still be uncomfortable enough for its threshold to have dropped, and lameness is a late sign rather than an early one.

3. Arousal, Threshold and Performance

3.1 The Threshold Is Real and Individual

Above a certain level of arousal, dogs stop taking food, stop responding to familiar cues, and stop orienting to the handler. That much is uncontroversial in practice. What is often added — a universal inverted-U curve in which moderate arousal is optimal for everyone — is not supported.

The frequently cited Yerkes–Dodson original trained dancing mice in a discrimination task with electric shock, and the most favorable shock strength depended on how difficult the discrimination was: with an easy discrimination, learning got faster as the shock got stronger across the range tested, while with harder discriminations an intermediate strength worked best (Yerkes & Dodson, 1908). It was a finding about task difficulty, not a general law of performance. In dogs, the optimum appears to depend on where the individual starts: assistance dogs bred and trained for low arousal inhibited better when their arousal was increased, while pet dogs starting from a higher baseline performed worse (Bray et al., 2015). The authors read this as consistent with an inverted U on which dogs start at different points. There is no single threshold to train toward, only this dog's (which is where stable individual differences come in).

3.2 The Threshold Moves

It is lowered by poor or insufficient sleep (with measurable effects on canine memory and emotion), by accumulated stress, by pain, and by what has already happened that day. This is why the same trigger at the same distance produces an outburst on Tuesday and nothing on Wednesday, and why owners describe the behavior as unpredictable when it is state-dependent (the arousal picture in detail).

3.3 What "Cannot Listen" Actually Means

The claim that a dog above threshold is physically incapable of hearing its handler overstates the case. A more cautious description is narrower: attention narrows toward the salient stimulus, and competing responses become less likely to win. The dog is not deaf. The cue is losing a competition it usually wins (which is the difference between trained behavior and emotional response).

3.4 Why the Threshold Is the Practical Center of This Article

Almost every recommendation here reduces to working below it and almost every failure to working above it. That is unglamorous and it is what the canine arousal evidence supports. Most technique disputes in this area are downstream of whether the dog was worked below its threshold, and that question is rarely the one being argued about.

The difficulty is that the threshold is not a distance, moves between days, and can only be confirmed after the fact by how quickly the dog recovers. Handlers who want a number are asking for something the variable does not have.

4. Threat Processing: What Canine Neuroimaging Shows

4.1 The Amygdala Is Not the Fear Center

The amygdala is involved in threat processing. Calling it the fear center implies a one-to-one mapping between a structure and an emotion that the evidence does not support, in dogs or in any species.

What canine work has shown is narrower and more useful. Using awake fMRI, dogs rated as more aggressive on a standardized owner questionnaire showed greater amygdala activation while watching their caregiver give food to a realistic fake dog, and that amygdala response habituated when the interaction was observed repeatedly (Cook, Prichard, Spivak & Berns, 2018). The habituation finding is the practically relevant one: the response is not fixed.

4.2 Frontal Inhibition Has Been Measured in Dogs

The claim that a prefrontal system supports impulse control in dogs is one of the few in this area with direct canine evidence. Thirteen dogs completed a go/no-go task inside the scanner and an A-not-B task outside it. A frontal region showed elevated activity during successful inhibition across all subjects, and dogs with greater mean activation in that region produced fewer false alarms (Cook, Spivak & Berns, 2016).

That is a genuine neural correlate of individual differences in canine self-control (examined further in the canine self-control literature). It also has limits: thirteen dogs, a laboratory task, and no measurement taken during an actual leash outburst.

4.3 "Amygdala Hijack" and the Two-Brain Story

The idea that emotional arousal takes the prefrontal cortex "offline" and hands control to a survival system is a popular framing borrowed from human self-help writing. It has not been measured in dogs. No study has imaged a dog during a reactive episode, and the awake-fMRI paradigm requires a dog to lie still and calm — which structurally excludes exactly the state the model describes.

The "thinking brain versus survival brain" dichotomy carries the same problem. It is a serviceable teaching metaphor and it is not a description of canine neuroanatomy. Presenting it as one is where most articles on reactivity leave the evidence behind.

4.4 Why Correcting the Popular Neuroscience Matters

The amygdala-hijack story and the two-brain account circulate widely in dog training and produce a specific consequence: they present the reactive dog as temporarily incapable rather than as an animal whose behavior depends on arrangeable conditions. The first framing leads to waiting; the second leads to changing the arrangement.

The canine imaging work supports a more useful picture, in which inhibitory control varies between individuals and with circumstances (Cook, Spivak & Berns, 2016) and arousal and control are not simply opposed (Bray et al., 2015).

4.5 What the Imaging Does Not Establish

Awake canine fMRI has measured individual differences under controlled conditions with scanner-trained dogs. It has not measured anything during a reactive episode, and it cannot: the situation requires a freely moving animal.

What the imaging supports is the correction of the popular account rather than a positive account of what happens on a walk. Those are different contributions and the first is the one this literature makes.

5. The Stress Response: Two Systems, Two Timescales

5.1 The Correction

Adrenaline and cortisol are routinely described together as products of the HPA axis. They are not, and the distinction matters for interpreting behavior.

Adrenaline is released via the sympathetic nervous system and acts within seconds: heart rate rises, muscles tense, the body is prepared for immediate action. Cortisol is released via the hypothalamic–pituitary–adrenal axis and takes minutes to reach meaningful concentrations, with effects that persist far longer. Conflating them collapses two different timescales into one and produces the mistaken impression that a cortisol measurement captures the moment of the outburst.

5.2 Why the Timescales Matter in Practice

The sympathetic response is what you see during the lunge. The HPA response is what is still elevated on the walk home, and what accumulates across a week of daily encounters (with the chronic picture examined separately).

This is the physiological basis for spacing exposures rather than working a dog through repeated triggers in one session — not because a single event is damaging, but because the second system has not returned to baseline when the next trigger arrives.

5.3 What Has Been Measured in Dogs

Beerda and colleagues exposed ten dogs to six different aversive stimuli and recorded both salivary cortisol and heart rate, establishing that acute stressors produce measurable endocrine and cardiac responses in this species (Beerda et al., 1998). Ten dogs is a small sample, and the stimuli were experimental rather than naturalistic — but it remains one of the few canine datasets combining both measures under controlled conditions.

5.4 Why the Two Timescales Explain the Bad Afternoon

A fast response that resolves in minutes and a slower one that persists for hours means a dog can be behaviorally recovered and physiologically not. The second encounter of the afternoon therefore starts from a different baseline than the first.

That is the mechanism behind what households describe as a dog having a bad day, and it is the argument for spacing rather than for persistence (how successive triggers add up across a walk). Two walks with four hours between them are not the same exposure as two walks with twenty minutes between them.

6. Learning History: Conditioning and Sensitization

6.1 Two Different Processes

Repeated exposure to a stimulus can reduce responding, which is habituation, or increase it, which is sensitization. According to dual-process theory, the two processes develop independently and interact to produce the behavior that is finally observed (Groves & Thompson, 1970). Intensity affects which one shows: the weaker the stimulus, the faster and more pronounced the response decrement, and very intense stimuli may produce no observable decrement at all (Rankin et al., 2009).

This helps explain a good deal of failed exposure work. Walking a fearful dog past other dogs every day is an intervention whose outcome depends heavily on whether the distance kept the intensity low enough for habituation to be possible (which is what a graded protocol controls for).

6.2 Conditioned Associations

A previously neutral stimulus paired with an aversive event can come to elicit a response on its own. In practice, the trigger set can widen over time, for example from one specific dog to dogs of that color to dogs generally (the canine fear-learning evidence).

Worth noting: a conditioned response that has been successfully reduced can return with time, with context change, or after a single re-exposure (which is why relapse is the expected pattern rather than a failure).

6.3 The Behavior Is Also Reinforced

The outburst often produces a consequence that can maintain it. The other dog passes, the handler turns and leaves, the distance increases. Whatever the emotional driver, a response followed reliably by that outcome can be reinforced by it. Whether it is depends on which consequence actually follows and what function the behavior serves for this dog — which is why treating reactivity purely as an emotional problem, with no attention to what the behavior achieves, tends to under-deliver.

6.4 Why Both Processes Can Run at Once

A dog on leash encountering another dog can be classically conditioned to the sight of the other dog and operantly reinforced by the other dog leaving. Plans that address only one of those can stall for reasons nobody can see. A counterconditioning plan that never arranges for the other dog to stay rather than leave is treating half the problem.

Which one dominates differs between cases, and the question is answerable: if the display continues after the target has gone, the operant account is weaker. That single observation is worth more than a description of the display itself.

7. Frustration as a Separate Route

7.1 The Same Topography, the Opposite Motivation

A sociable dog restrained from reaching another dog produces barking, lunging and pulling that is behaviorally hard to distinguish from the fearful version. The motivation is approach, not avoidance.

Frustration in dogs is studied experimentally by withholding an expected reward or making a previously accessible resource inaccessible. In one such study the reward was unreachable in a non-social setup and withheld by a non-complying experimenter in a social one, and the dogs' responses differed, among other things, with their rank in multi-dog households (Vékony, Bakos & Pongrácz, 2024). The lead is the blocking agent in most reactive presentations, which makes on-lead frustration a plausible and frequently encountered route rather than an exotic one (with the underlying neurobiology covered separately).

7.2 How to Tell Them Apart

Not by the outburst. By what happens when the barrier is removed under safe conditions, by body orientation and weight distribution during the episode, by whether distance reduces or intensifies the behavior, and by the dog's history with the trigger class. None of these is diagnostic alone; together they usually resolve it.

7.3 Why Getting It Wrong Is Costly

Distance work is the standard prescription, and on its own it does not resolve the core problem in a frustration case. Distance can still lower arousal, prevent rehearsal and create room to train alternatives, but it does not change the fact that the behavior is directed toward the trigger rather than away from it. The corresponding error runs the other way: giving a fearful dog access in order to "let them sort it out" places it in exactly the situation its behavior was designed to prevent.

7.4 Why Frustration Is the Underdiagnosed Route

Fear is the explanation practitioners often reach for first, and the frustrated dog presents with the same topography while its behavior is directed the opposite way. Distance addresses the core of the fearful case but, on its own, not the frustrated one, which is why a plan that relies on distance alone can plateau quickly there. If distance is all the plan offers and no alternatives are built, it can add frustration and make matters slightly worse while appearing conservative.

A useful clinical discriminator, though not a validated one, is what the dog does when it can leave: a frightened dog tends to take the option and a frustrated one tends not to. Arranging a situation where leaving is genuinely available is the test, and a lead removes it by design.

8. Reactivity Versus Aggression, and What Follows for Training

8.1 The Overlap Is Partial

Reactive displays are frequently driven by emotional overload rather than by an intent to close distance and cause harm. That is the useful core of the distinction, and it is why "reactive" is a kinder and often more accurate description than "aggressive."

It should not be overstated. Some reactive dogs would bite if the distance closed, and the categories are not mutually exclusive. Notably, human-directed aggression in different contexts largely fails to co-occur within individual dogs, which supports a situational reading of both phenomena rather than a trait reading (Casey et al., 2014).

8.2 What Dominance Framing Does Here

Interpreting a leash outburst as a rank challenge leads directly to confrontational handling, and the evidence points clearly in one direction: confrontational methods elicited an aggressive response from at least a quarter of the dogs on which they were tried in a referral population (Herron, Shofer & Reisner, 2009). Owner-reported use of positive punishment or negative reinforcement is associated with substantially higher reported aggression (Casey et al., 2014), and aversive-based methods are associated with poorer welfare outcomes more broadly (Vieira de Castro et al., 2020; Casey et al., 2021) (with the neurological consequences examined in depth; and the construct itself assessed here).

Beyond the welfare argument there is a mechanical one: suppressing the display removes the warning while leaving the underlying state in place.

8.3 Management First, Training Second

Management and training are different tools with different jobs. Management changes the situation so the outburst does not happen — route planning, distance, visual barriers, timing walks away from peak traffic, a longer lead in open space. Training changes what the dog does in the situation. Owners are routinely told management is avoidance and that the real work is training, which gets the order exactly backwards.

Two mechanisms already established above explain why. Repeated exposure at high intensity does not reliably produce habituation (Rankin et al., 2009) and can sensitize responding (Groves & Thompson, 1970), so each outburst can contribute to making the next one more likely. And the display can be reinforced by its outcome when the trigger passes and the distance increases, in which case every rehearsal strengthens the behavior independently of the emotional driver. An unmanaged dog is therefore not necessarily standing still while training proceeds; it can get worse in both channels between sessions.

Management is what stops that. It is not a substitute for training and it is not a permanent state, but training conducted without it is being run against processes that can undo its progress.

8.4 What the Evidence Supports Doing

Work at an intensity at which habituation is possible rather than above it. Space exposures so the slower stress system returns to baseline. Identify whether the driver is fear or frustration before deciding whether distance is enough or the plan also needs alternatives and controlled approach. Rule out pain when the behavior is new or has changed in character. And evaluate outcome by whether the dog's state has changed rather than by whether the display has stopped (a distinction suppression makes easy to miss; and anxiety complicates further).

8.5 What the Overlap Means for Risk

Reactivity is not aggression and reactive dogs do sometimes bite. The risk plausibly rises when the display has been repeatedly suppressed or when distance is unavailable — a cornered dog on a short lead has neither option the display was directed at. Treating the two as unrelated understates the risk; treating them as the same overstates it.

The practically useful position is that the display provides information, the risk rises when that information stops having an effect, and management exists to prevent that situation (what a display does and does not reveal). A household that understands that treats the lunging as information rather than as the problem to be eliminated.

9. What to Ask in a First Consultation

9.1 When Did It Start and What Changed

Onset and what accompanied it separate a developmental pattern from an acquired one and from a medical one. A behavior that appeared over three weeks in an adult dog has a different differential from one present since adolescence. The first is a medical question until shown otherwise; the second is usually developmental.

9.2 What Exactly Does the Dog Do

Not "he reacts" but the sequence: what the dog does first, what follows, what it does with its weight, whether the display escalates or holds. The sequence distinguishes routes that the summary word conceals.

9.3 What Has Already Been Tried

Where confrontational methods have been used, the history includes their effects, and the dog in front of you is not the dog the household started with. Owner-reported aggressive responses to such techniques are common (Herron et al., 2009), and their presence changes the plan.

Asking without implying criticism is a skill worth having, because households that feel judged report less, and an incomplete history produces a plan built on the wrong case.

9.4 What Does the Week Look Like

How many encounters occur, how much recovery falls between them, and whether the household can avoid the situation at all. A plan that requires management the household cannot deliver is a plan that will not run.

That question is asked last and frequently determines everything, because it establishes what is actually possible rather than what would be ideal. A household in a flat beside a busy park has different options from one with a garden and a quiet lane.

10. Which Findings Come From Which Species

10.1 An Unusually Canine Article

Nine of this article's twelve sources are canine, which is why it can correct several popular claims rather than only qualify them. That balance is unusual in this collection and it is what the subject required.

10.2 What Was Measured in Dogs

Individual differences in inhibitory control have been imaged in awake dogs (Cook, Spivak & Berns, 2016), and amygdala responses have been recorded in this species (Cook et al., 2018). The arousal-inhibition relationship was tested directly (Bray, MacLean & Hare, 2015), acute stress responses were characterized (Beerda et al., 1998), and human-directed aggression has been examined in a large survey (Casey et al., 2014).

Training method and welfare (Vieira de Castro et al., 2020; Casey et al., 2021), the outcomes of confrontational techniques (Herron, Shofer & Reisner, 2009) and behavior in frustrating situations (Vékony, Bakos & Pongrácz, 2024) are likewise canine.

10.3 What Was Established Elsewhere

The habituation characteristics come from comparative neuroscience (Rankin et al., 2009), the dual-process account from work on cats and rats (Groves & Thompson, 1970), and the original arousal-performance result from mice (Yerkes & Dodson, 1908). The habituation characteristics are described as seen across all species studied (Rankin et al., 2009), and the Yerkes–Dodson study is cited here for what it did not show rather than as evidence about dogs.

10.4 Why That Balance Matters Here

This article makes corrective claims — that the amygdala is not a fear center, that the two-brain story is not a canine finding, that frontal inhibition has actually been measured in dogs. Those claims require canine evidence, and they have it. Correcting a popular neuroscience claim with a rodent study would invite the obvious reply.

An article correcting popular neuroscience with borrowed neuroscience would be in a weak position. This one is not, which is worth stating because the correction is the article's main contribution.

10.5 Where the Canine Evidence Runs Out

No canine study has imaged a dog during a reactive episode on a walk, measured the neural difference between fear-driven and frustration-driven displays, or followed reactive dogs longitudinally through treatment. The first is impossible with current methods; the other two are not.

The distinction this article rests on — fear against frustration — is supported behaviorally and has not been demonstrated neurally in this species. That is sufficient for the practical claims and insufficient for any claim about what is happening in the brain.

11. Summary at a Glance

"Reactivity" is a practitioner term — No standard operational definition, no validated measure, no prevalence figure. It describes what the handler sees, not what the dog is doing.

The threshold is individual, not universal — Increasing arousal improved inhibition in low-arousal assistance dogs and impaired it in higher-arousal pet dogs (Bray et al., 2015); the original Yerkes–Dodson result depended on task difficulty (Yerkes & Dodson, 1908).

Canine neuroimaging supports frontal inhibition — A frontal region tracked successful response inhibition across thirteen dogs, and greater activation was associated with fewer false alarms (Cook, Spivak & Berns, 2016).

Amygdala responses habituate — More aggressive dogs showed greater amygdala activation to a social resource threat, and that response declined with repeated exposure (Cook et al., 2018).

Adrenaline and cortisol are not the same system — Adrenaline via the sympathetic nervous system in seconds; cortisol via the HPA axis over minutes, with longer persistence.

Intensity shapes whether repetition calms — Weaker stimuli habituate faster and very intense stimuli may not habituate at all (Rankin et al., 2009), while sensitization runs as a separate process alongside (Groves & Thompson, 1970).

Fear and frustration look alike and are not alike — Frustration is produced experimentally by making an available reward suddenly inaccessible (Vékony et al., 2024); on leash, the lead is the blocking agent.

Management first, training second — Unmanaged outbursts can sensitize responding and reinforce the behavior at the same time, so an unmanaged dog can get worse between sessions rather than holding steady.

Confrontation raises risk — Confrontational methods elicited aggression from at least a quarter of dogs on which they were used (Herron et al., 2009).

12. Research Gaps and Critical Appraisal

No dog has been imaged during a reactive episode. Every neuroimaging claim in this area is inferred from dogs lying still in a scanner in a calm state. The awake-fMRI method structurally cannot capture the state that the popular model describes, and no article on reactivity — including this one — can honestly claim otherwise.

"Amygdala hijack" and the two-brain model are borrowed, not measured. Both come from human popular psychology. They may turn out to be roughly right. They are currently metaphors presented as mechanism.

Canine neuroimaging samples are very small. Thirteen dogs is typical, subjects are self-selected volunteers trained to tolerate a scanner, and that population is unlikely to represent dogs with severe reactive presentations.

Neuroplasticity claims are the weakest link. The assertion that training builds new neural pathways supporting calmer responses is plausible on general mammalian grounds and has not been demonstrated in dogs. Behavioral improvement is well documented; the neural account of it is not.

The fear–frustration distinction lacks a validated test. It is currently made through clinical judgment using converging signs and has not been demonstrated neurally in this species. No standardized instrument distinguishes the two, which means the most consequential decision in a reactivity case rests on the least formalized part of the assessment.

Prevalence is unknown. Because the term is undefined, there is no meaningful figure for how many dogs are affected, and any number quoted elsewhere should be treated as an estimate of something else.

Most supporting evidence is owner-reported and cross-sectional. The training-method associations in particular establish pattern rather than causation, and referral populations are not general populations.

Longitudinal outcome data are absent. How reactive dogs fare over years, with and without intervention, has not been followed systematically, so prognosis statements given in consultations rest on clinical impression.

13. Conclusion

The standard neurological account of the lunging dog is roughly the right shape and considerably more confident than the canine evidence permits. Frontal regions supporting inhibition have been located in dogs, amygdala responses to social threat have been measured and shown to habituate, and stress physiology in dogs is documented — but no dog has ever been scanned mid-outburst, the "amygdala hijack" is imported from human self-help rather than measured in this species, and the neuroplasticity story that usually closes these articles is an extrapolation with no canine data behind it. What survives scrutiny is more useful than what does not. The threshold is real and individual rather than universal. Intensity shapes whether repeated exposure calms a dog or fails to, which makes distance a mechanism rather than a courtesy. Adrenaline and cortisol run on different systems and different clocks, which is why spacing exposures is physiology rather than caution. And the single most consequential judgment in any reactivity case — whether the dog's behavior is directed at getting away or at getting there — is made on clinical signs rather than on any validated instrument, which is worth stating plainly rather than obscuring behind neuroscience that sounds more settled than it is.

Key Insights (Takeaways)

• "Reactivity" is not a scientific category. It has no agreed operational definition, no validated measurement, and no prevalence figure — unlike aggression, which research defines operationally so that studies count the same thing (Casey et al., 2014). The word describes what the handler experiences and bundles together at least four different problems: fear, frustration, elevated baseline arousal, and pain.

• Fear and frustration produce near-identical outbursts from opposite motivations. Frustration is produced experimentally by making a previously available reward suddenly inaccessible (Vékony et al., 2024); on leash, the blocking agent is the lead itself. Distance work is the standard prescription and on its own does not resolve the core problem in a frustration case, which is one plausible reason a reactivity plan produces no change.

• Intensity shapes the outcome of exposure as much as repetition does. Weaker stimuli habituate faster and very intense stimuli may not habituate at all (Rankin et al., 2009), while sensitization runs as a separate, incremental process (Groves & Thompson, 1970). Walking a fearful dog past triggers daily is therefore not neutral practice; its direction depends heavily on distance.

• Adrenaline and cortisol are different systems on different clocks. Adrenaline acts within seconds via the sympathetic nervous system; cortisol takes minutes via the HPA axis and persists far longer. The widespread claim that the HPA axis releases both is wrong, and it is the reason spacing exposures is a physiological argument rather than a stylistic preference.

• The neuroimaging is real but thinner than it sounds. A frontal region tracked successful inhibition across thirteen dogs, with greater activation associated with fewer false alarms (Cook, Spivak & Berns, 2016), and amygdala responses to social threat habituated with repeated exposure (Cook et al., 2018). No dog has been scanned during an actual reactive episode, and the "amygdala hijack" remains a borrowed metaphor rather than a canine finding.

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