Because dopamine isn’t “more = better.” It’s a gain control / gating chemical. Turn the gain up too high and the system starts firing off half-cooked decisions like a group chat at 2 a.m. Here’s the clean neuro story for jumpy or inconsistent timing (and why it can show up as jumpy, inconsistent movement too).

1. Dopamine pushes the basal ganglia toward “GO” too easily In the basal ganglia, you’ve basically got: a Go pathway (often simplified as D1-favored) that helps initiate actions/sequences a No-Go pathway (often simplified as D2-favored) that helps suppress competing actions

Higher dopamine tends to bias selection toward Go and reduce braking. If it’s too high (or too noisy), the threshold for “initiate” drops. Result: premature starts, extra micro-corrections, more switching, less stable pacing. That’s the “jumpy” part: the system keeps saying “NOW” before it’s fully settled on what “now” means. 2) Too much dopamine can reduce signal-to-noise (especially if it’s tonic) There’s phasic dopamine (brief bursts: “important event / prediction error!”) and tonic dopamine (baseline level). If tonic dopamine is too high: receptors and downstream circuits can get closer to saturation phasic changes become less informative relative to the baseline neural activity can become more variable because the network is operating in a high-gain regime

Result: timing feels less consistent, because the internal “when” signal jitters. 3) Inverted-U: optimal dopamine exists, and it’s not at the top A lot of dopamine-dependent functions follow an inverted-U: too low → sluggish initiation, slow internal pacing optimal → stable timing, good gating too high → impulsive gating + noisier control

So “too much” can make you fast-but-wrong, then constantly correcting, which looks like variability. 4) The internal clock can speed up (and get messier) In classic timing models (pacemaker/accumulator style), dopamine tends to speed the internal clock (more “ticks” per second). That means: intervals can feel longer than they are you may respond too early (like you swear it’s been long enough) if dopamine is also noisy, the tick rate varies, producing inconsistent estimates

Result: jumpy timing and variable rhythm. 5) Movement example: why running can look “jittery” Running is a rhythmic motor program, but it still needs continuous gating and error correction: basal ganglia help select and maintain the motor pattern dopamine affects how easily you switch patterns or make corrections

Too much dopamine biasing “Go” can produce: over-correction (tiny unnecessary adjustments) inconsistent stride timing trouble holding a steady cadence unless externally paced

(And yes, cerebellum and sensory feedback also matter, but dopamine can absolutely make the whole thing feel twitchy.) The punchline High dopamine (or unstable dopamine signaling) can make the basal ganglia: trigger actions too readily switch too easily encode timing with more variability turn “smooth prediction” into “impulsive guesses + corrections”

So you get jumpy timing: not just “faster,” but less stable. If you want a very practical mental model: dopamine is the “commit” button. Too little and you can’t press it. Too much and you press it 12 times, then undo half of it.