Working memory is imprecise, and these imprecisions can be explained by the combined influences of random diffusive error and systematic drift toward a set of stable states (“attractors”). However, the neural correlates of diffusion and drift remain unknown. Here, we investigated how delay-period activity in frontal and parietal cortex, which is known to correlate with the decline in behavioral memory precision observed with increasing memory load, might relate to diffusion and drift. We analyzed data from an existing experiment in which subjects performed delayed recall for line orientation, at different loads, during functional magnetic resonance imaging (fMRI) scanning. To quantify the influence of drift and diffusion, we modeled subjects’ behavior using a discrete attractor model and calculated within-subject correlation between frontal and parietal delay-period activity and whole-trial estimates of drift and diffusion. We found that although increases in frontal and parietal activity were associated with increases in both diffusion and drift, diffusion explained the most variance in frontal and parietal delay-period activity. In comparison, a subsequent whole-brain regression analysis showed that drift, rather than diffusion, explained the most variance in delay-period activity in lateral occipital cortex. These results are consistent with a model of the differential recruitment of general frontoparietal mechanisms in response to diffusive noise and of stimulus-specific biases in occipital cortex.

工作记忆是不精确的，这些不精确性可以通过随机扩散误差和朝向一组稳定状态（“吸引子”）的系统漂移的综合影响来解释。然而，扩散和漂移的神经相关性仍然未知。在这里，我们研究了额叶和顶叶皮层的延迟期活动如何与扩散和漂移相关，众所周知，额叶和顶叶皮层的延迟期活动与随记忆负荷增加而观察到的行为记忆精度下降相关。我们分析了现有实验的数据，在该实验中，受试者在功能磁共振成像 (fMRI) 扫描过程中，在不同负载下对线方向进行延迟回忆。为了量化漂移和扩散的影响，我们使用离散吸引子模型对受试者的行为进行建模，并计算额叶和顶叶延迟期活动与漂移和扩散的整个试验估计之间的受试者内相关性。我们发现，尽管额叶和顶叶活动的增加与扩散和漂移的增加相关，但扩散解释了额叶和顶叶延迟期活动的最大差异。相比之下，随后的全脑回归分析表明，漂移而不是扩散解释了枕叶皮质延迟期活动的最大差异。这些结果与一般额顶叶机制响应扩散噪声和枕叶皮层刺激特异性偏差的差异招募模型一致。