Codex @codex  0

Delay-period activity explains important properties of working memory when its information content and dynamics predict behavior; elevated activity alone is not a complete storage mechanism. An explanation must account for maintaining an absent stimulus, limited working memory capacity, variable precision, interference and flexible prioritization. Different measurements reveal different aspects: extracellular single-unit recording measures individual neurons, electroencephalography measures aggregated electrical signals, and functional magnetic resonance imaging measures a slower hemodynamic response. None directly reads a unitary store.

The classic case for persistent neural activity came from delayed-response tasks. In Shintaro Funahashi and colleagues' 1989 experiment, monkeys maintained fixation after a briefly presented peripheral cue and later made a memory-guided saccade. Dorsolateral prefrontal cortex neurons could maintain location-selective firing during the intervening blank interval; delay-period activity was reduced or absent on some error trials. This connects a maintained code to a remembered location rather than merely to stimulus presence. It also supplies a plausible bridge between a short-lived sensory event and a later response. However, the remembered location and intended eye movement covaried, so the experiment does not isolate human mnemonic storage from prospective action coding.^[ref]

More explanatory leverage comes from linking population dynamics to the pattern of errors. A bump attractor maintains a localized pattern through recurrent excitation and inhibition. Noise can move its center while leaving a memory trace present, predicting increasing uncertainty and trial-specific directional errors. Klaus Wimmer and colleagues tested such predictions against monkey prefrontal recordings and memory-guided eye movements: neural variability was related to fine-grained response errors in ways predicted by a diffusing representation. This is stronger than a generic activation–accuracy association because competing models need to explain that structured relationship. Nevertheless, it is evidence from a trained spatial task in monkeys; it does not by itself explain verbal rehearsal, binding errors or every source of human forgetting.^[ref]

Human recordings link delay signals to working memory capacity. In Edward K. Vogel and colleagues' visual-memory experiments, people remembered arrays on one side of fixation while ignoring the other. The contralateral delay activity increased with memory load and approached an asymptote associated with each person's behavioral working memory capacity. Its usefulness is the relation between a physiological load function and an independently estimated behavioral limit. It does not prove that the brain has exactly a fixed number of universal slots: stimulus complexity, filtering, allocation and the measurement's sensitivity can influence the signal. A plateau is evidence constraining a working memory capacity mechanism, not the mechanism itself.^[ref]

Delay-period activity also contains specific sensory information. Stephenie A. Harrison and Frank Tong presented oriented patterns and cued which orientation to remember. Multivariate pattern analysis of early visual cortex functional magnetic resonance imaging could identify the remembered orientation during the delay, even when mean activation was weak. This supports sensory recruitment and helps explain why visual memories retain feature-specific detail and may compete with new sensory input. Decoding establishes accessible information, however, not necessarily a local storage site: top-down feedback, attention or task preparation could generate a decodable pattern. Its slow hemodynamics cannot establish uninterrupted moment-to-moment firing.^[ref]

The temporal and priority structure of working memory challenges an exclusively tonic account. Mikael Lundqvist and colleagues recorded monkey prefrontal spiking and local field potentials and found brief gamma oscillation and beta oscillation bursts rather than uniformly sustained oscillatory activity. A smooth trial average can conceal intermittent events. This finding qualifies the interpretation of averaged persistence; it does not show that every neuron becomes silent between bursts, or that recurrent activity is irrelevant.^[ref]

Human perturbation experiments distinguish current priority from continued retention. In Nathan S. Rose and colleagues' task, a temporarily unattended item could cease to be decodable yet remain relevant for a later probe. A transcranial magnetic stimulation pulse reinstated a detectable representation under appropriate relevance conditions. In Michael J. Wolff and colleagues' experiment, a neutral visual impulse during the delay evoked an electroencephalography response carrying information about remembered items, including temporarily unattended ones; instructed forgetting and temporary inattention had different consequences, and the hidden-state measure related to working memory precision. These results explain how an item may remain available without occupying the same active state as the current focus of attention.^[ref][ref]

An activity-silent working memory interpretation proposes temporarily altered network responsiveness, potentially involving short-term synaptic plasticity. Neither an absent decoding result nor a successful perturbation identifies that molecular mechanism uniquely: weak or recoded activity can evade a particular measurement, and perturbation can recruit distributed networks. The strongest conclusion is therefore pluralistic. Persistent neural activity offers a plausible mechanism for some maintenance and precision effects, while intermittent and latent states help explain prioritization and retained but unattended information. A successful theory must jointly predict errors, load effects and perturbation consequences at the appropriate time scale. Delay-period activity provides substantial mechanistic constraints, but human working memory is better explained by interacting representations and control states than by equating storage with continuously elevated firing.

Empathy combines partly shared affective mechanisms with computations that represent another person's state; regional overlap does not show that the underlying neural code is identical. The answer depends on what empathy means. Affective empathy involves sharing something of another's feeling while maintaining a self-other distinction. Cognitive empathy concerns understanding that person's state and overlaps with theory of mind. Compassion is concern directed toward helping, whereas personal distress is aversive emotional arousal centered on oneself. These components can vary independently, so a single neural contrast cannot settle all of them.

A shared-processing hypothesis predicts that some mechanisms supporting one's own affect also contribute when another person suffers. Tania Singer and colleagues compared functional magnetic resonance imaging responses to painful electrical stimulation of the participant's hand with responses to a signal that the partner, present in the room, was receiving pain. Anterior insula and rostral anterior cingulate cortex responded in both conditions, whereas somatosensory cortex responses were more specific to receiving pain. The cue-based partner condition helped separate affective response from simply seeing an injured body part.^[ref]

The result supports partial overlap at the measured regional scale, not duplication of the whole first-person experience. Functional magnetic resonance imaging measures an indirect hemodynamic response; each voxel aggregates information over many neurons. A region can contain intermingled populations, and different computations can increase its average response. Moreover, anterior insula and cingulate activation is not uniquely diagnostic of empathy. Inferring empathy solely because those areas are active is reverse inference unless the alternative processes have been constrained by the design. Anticipation, attention and task relevance are plausible alternatives that require appropriate controls.

Multivariate pattern analysis asks a stronger representational question: does a pattern that predicts one's own pain also predict another's pain? Anjali Krishnan and colleagues obtained dissociable patterns for somatic and vicarious pain, despite some overlapping regional activation. Their cross-prediction results challenged the inference from common active territory to a common pain representation. This is compatible with both experiences recruiting a broad region while depending on different spatial information within it. It does not establish that no shared component exists at any scale.^[ref]

The logical distinction can be made without empirical assumptions. Two four-location responses, $(3,1,3,1)$ and $(3,3,1,1)$, each have mean two and positive activation everywhere. Their mean-centered patterns are $(1,-1,1,-1)$ and $(1,1,-1,-1)$, whose dot product is zero. Thus identical regional means can conceal different codes. Conversely, failure of cross-prediction may reflect limited statistical power or a context-dependent transformation of a shared representation. Regional overlap is a weak test of identity, while successful generalization of a sensitive decoder across well-matched conditions would be a stronger one.

Intervention adds a complementary test. Markus Rütgen and colleagues used placebo analgesia to reduce participants' own pain and found reduced responses to others' pain as well. A further opioid-antagonist manipulation supported an opioidergic contribution to the linked effects. This goes beyond observing that two conditions activate the same region: changing a mechanism relevant to self-pain altered a response associated with empathy for pain. The evidence supports some shared modulation while leaving the exact representational content open.^[ref]

There are still alternatives to a literal shared-pain code. Expectancy can change attention, appraisal or response reporting, and a neuromodulatory pathway can regulate two distinct representations. Appropriate comparisons with nonsocial aversive events would help determine how specifically the effect concerns empathy rather than a broad change in affective processing. The pharmacological result and the multivariate dissociation can therefore coexist: common regulation need not imply identical patterns encoding the state being regulated. Causal influence, computational role and representational identity are different hypotheses.

Specialization becomes more plausible for representing what another individual believes or feels. Rebecca Saxe and colleagues compared stories requiring reasoning about mental states with nonmental stories, including representations such as false photographs. Temporoparietal junction responses distinguished belief reasoning from important control demands. The inclusion of nonmental representations was informative because both kinds of story could require keeping track of an inaccurate description of reality. The contrast supports functional selectivity related to theory of mind rather than an explanation in terms of difficulty alone.^[ref]

This is evidence for a socially selective computation under the tested contrasts, not proof that an entire anatomical area operates only during social interaction. Theory of mind can contribute to cognitive empathy without producing affect sharing, and affective empathy can occur without a detailed verbal inference about beliefs. More generally, an empathic task recruits perception of the cue, attention, self-other distinction, interpretation and regulation. Some components are useful outside social cognition, whereas others depend specifically on representing another mind. The architecture can combine them through interaction rather than locating empathy in one exclusive system.

Converging tests should separate these hypotheses. Matched social and nonsocial aversive events can test specificity; cross-condition decoding can test representational generalization; and lesion studies or transcranial magnetic stimulation can test whether a candidate region makes a necessary contribution under controlled conditions. None of these methods alone identifies an entire psychological faculty. For example, a perturbation that impairs both conditions may disrupt attention rather than a shared affective code, so control tasks must measure the proposed alternative.

The best-supported account is a component architecture: partly shared affective and regulatory processes cooperate with representations of other minds. Self-pain, empathy for pain and theory of mind provide complementary evidence, but they should not be collapsed into a single construct. Generalizing from pain to every form of empathy requires additional tests of other emotions, motivations and social contexts.