Both humans and animals have the ability to learn from past experience and to adapt
their behavior to resolve future conflicts faster or avoid them entirely. Conflicts in
spatial stimulus–response tasks occur when the origin of the stimulus and the response
area differ in location. Those conflicts lead to increased error rates, reaction times (RT)
and movement time (MT) which has been termed Simon effect. A model of dual route
processing (automatic and intentional) of stimulus features has been proposed,
predicting response conflicts if the two routes are incongruent. Although there are
various theories related to underlying neuronal mechanisms, it is commonly assumed
that the anterior cingulate cortex (ACC) plays a crucial role in conflict and error
processing. The Simon task is a neuropsychological interference task commonly used to
study performance monitoring. Interestingly, the resulting conflict is far from uniquely
human, as it has also been observed in pigeons, rats, and monkeys. On a neural level,
the on-going monitoring of correct and incorrect behavior appears in the form of eventrelated
potentials (ERPs). More precisely, the error-related negativity (ERN/Ne)
component of the resulting ERP, assumed to be generated in the ACC, is suggested to
reflect conflict and error monitoring. Unfortunately, there is often little correspondence
between human and animal studies. On this account the present study uses a modified
auditory Simon task to investigate a) the anatomical basis, b) the conflict- and errorrelated
electrophysiological correlates and c) the performance monitoring from a crossspecies
point of view.
By using positron emission tomography (PET) in combination with the metabolic tracer
[18F]fluorodeoxyglucose, which accumulates in metabolically active brain cells during
the behavioral task, we first aim at identifying relevant brain areas in a rat model of the
Simon task. According to the dual route model, brain areas involved in conflict
processing are supposed to be activated when automatic and intentional route lead to
different responses (dual route model). Results show specific activation patterns for
different task settings coherent with the dual route model. Our data suggest that the rat
motor cortex (M1) may be part of the automatic route or involved in its facilitation,
while premotor (M2) and prelimbic areas, as well as the ACC appear to be essential for
inhibiting the incorrect, automatic response, indicating conflict monitoring functions.
Interestingly, our findings remarkably fit the pattern of activated regions reported during
conflict processing in humans. To further support our findings, we measured local field
potentials (LFP) from electrodes centered in the rat ACC. LFPs showed a negative slow wave less pronounced for errors at about 250-400 ms after reaction. Stimulus-locked
data revealed a compatibility effect in rats, with a negative slow wave with onset in the
latency range of the reaction. To finally compare these results with a human setup, we
also developed a translational task for humans. In both species, similar behavioral
effects were found, including an increase in error rate, RT and MT. In humans, although
no difference in EEG amplitude between errors and hits in the ERN latency range was
found, a pronounced error positivity between 250 and 350 ms after reaction was seen.
Humans surprisingly demonstrated a stronger negativity for compatible compared to
incompatible trials. Similarly to rats, this effect started at about the time of reaction
time. Thus, both species (i) showed electrophysiological responses differentiating
between errors and correct in a similar latency range, (ii) demonstrated a valid
occurrence of the Simon effect and seem to pursue similar response strategies, both in
terms of RT and MT and (iii) displayed sustained differences in the modulation of the
ERP depending on correct or incorrect responses starting at the time of response and
prior to reward/no reward. It is thus tempting to speculate that the underlying cognitive
error processing mechanisms are highly similar across species.
In conclusion, we found remarkable behavioral, electrophysiological and functional
similarities between rat and human conflict and error processing. Our paradigm offers a
new approach in integrative, cross-species research and provides a useful rodent model
for investigating performance monitoring
