We conclude that corticolimbic regulation of emotion might be more effective at modulating motivation components than at modulating hedonic reactions to the impact of emotional events.
These considerations suggest an additional qualitative difference between glutamatergic versus GABAergic hyperpolarizations, beyond a simple intensity difference, which may also contribute to differing modulation of hedonic reactions to sensory pleasure or displeasure.
Supporting a keyboard-like pattern of affective modulation, muscimol produced progressively greater suppression of positive hedonic reactions elicited by oral infusions of sucrose-quinine solution as sites became progressively more caudal (correlation of hedonic suppression with caudal placement: r(25) = .461, p = .023).023
Notably, specific musical anhedonics showed similar hedonic reactions, both behaviorally and physiologically, as the HDN control group in both tasks.
Muscimol microinjections shifted the positive hedonic impact of tastes in a keyboard-like gradient pattern, at rostral levels enhancing positive hedonic reactions but at more caudal levels suppressing the same positive hedonic reaction and instead amplifying aversive reactions to tastes (correlation of hedonic reaction change with rostrocaudal position = r (24) = 0.461, p<0.01).
Thus, we conclude that ionotropic AMPA glutamate disruptions in NAc shell do not modulate hedonic pleasure, but consider the hedonic role of metabotropic glutamate receptors to remain an open empirical question.
The sucrose-quinine mixture was used in order to elicit both positive hedonic reactions ('liking') and negative aversive reactions ('disliking') in the same session.
We conclude that the influence exerted by top-down controls over NAc may be limited to motivational states, and may leave core hedonic reactions to affective events relatively untouched.
Microinjection of muscimol at this rostral level in medial shell nearly doubled hedonic reactions to the sucrose-quinine mixture (muscimol = 34.3+/−5.88 SEM versus vehicle = 19.5+/−6.45 SEM tested at 15 min after microinjection; F(1.5) = 7.888, p = .038).038
Direct contrast of DNQX and muscimol effects confirmed that muscimol robustly altered hedonic reactions while DNQX did not (muscimol versus DNQX, site X drug interaction, 15 minutes, F 1,21) = 6.296, p = .020; 1 hr, F 1,21) = 6.957, p = .015).015
