Nevin & Grace invoke a behavioral metaphor from the physics of momentum. The idealized assumptions they invoke are argued to translate to behavior only in the limited case of steady-state, constant-probability VI responding. Rather than further refine this limit case, mathematical models should be applied to generalizations of the limit case itself, broadening our understanding of behavioral processes.

We used Nunez's physiologically based dynamic theory of EEG to make predictions about a clinical population of children with Attention Deficit Hyperactivity Disorder (ADHD) known to have neuronanatomical abnormalities. Analysis of high-density EEG data (long-range coherence) showed expected age-related differences and surprising regional specificity that is consistent with some of the literature in this clinical area.

Nevin & Grace present a fresh and thoroughly empirical argument undermining the traditional view of learning based on response contingent reinforcement. We endorse the main points in the target article and relate them to an ethological feed forward principle that complements the principle of behavioral momentum.

Simple heuristics are clearly powerful tools for making near optimal decisions, but evidence for their use in specific situations is weak. Gigerenzer et al. (1999) suggest a range of heuristics, but fail to address the question of which environmental or task cues might prompt the use of any specific heuristic. This failure compromises the falsifiability of the fast and frugal approach.

This commentary discusses three features of the general theoretical framework proposed by Nunez: (1) Functional concepts, such as computation and control, are not foundational. (2) A mismatch between the concept of subcortical input and EEG output is problematic for the input/output operator concept of cortical dynamics. (3) The concept of brain state is relatively static.

Arbib et al.'s comprehensive review of neural organization, over-relies on modernist concepts and restricts our understanding of brain and behavior. Reliance on terms like coding, transformation, and representation perpetuates a “black-box approach” to the study of the brain. Recognition is due to the authors for attempting to introduce postmodern concepts such as chaos and self-organization to the study of neural organization. However, confusion occurs in the implementation of “biologically rooted” schema theory in which schemas are viewed as computer programs. The inclusion of an additional functional level between structure and dynamics is unnecessary in a postmodernist perspective of brain and behavior.

Biologists recognize Pavlovian conditioning as a mechanism by which individuals can adaptively modify their social and nonsocial behavior quickly to relevant features of the natural environment. This commentary supports Domjan et al.'s point that psychologists could gain important insights by broadening the range of species and behaviors they study and by continuing to adopt a functional perspective to investigate Pavlovian conditioning and other forms of learning.

A new working hypothesis of sleep-wake cycle mechanisms is proposed, based on ontogeny and functional/anatomic compression of two stochastic neuronal models of information coding that complement each other in a key/lock fashion: the axonal arbor patterns (AAP – “hardware”) and the neuronal spike interval inequality patterns (SIIP – “software”).

[Hobson et al.; Nielsen; Revonsuo; Solms; Vertes & Eastman]

As reported by Vertes & Eastman, convincing evidence rules out any role for REM sleep in memory consolidation. However, they do not provide convincing evidence for their claim that sleep in generaI – as opposed to REM sleep per se – has no influence on memory consolidation. Recent correlational data suggest that the number of NREM/REM cycles is associated with performance on a verbal recall task.

[Vertes & Eastman]

Neural organization has many facets; multiple descriptive levels and multiple analytical strategies coexist. Although most neuroscientists agree that a multidisciplinary, multistrategic approach is necessary to understand neural organization, diverse individual approaches make it difficult to find the optimal mixture and priority list.

Pavlovian feed-forward mechanisms represent an individual perspective that ignores how repeated interactions between the same individuals lead to social relationships. These can determine social cues, coordinated behaviors, asymmetries between partners, and physiological and emotional states associated with social interaction.

This commentary focuses on three issues raised by Gigerenzer, Todd, and the ABC Research Group (1999). First, I stress the need for further experimental evidence to determine which heuristics people use in cognitive judgment tasks. Second, I question the scope of cognitive models based on simple heuristics, arguing that many aspects of cognition are too sophisticated to be modeled in this way. Third, I note the complementary role that rational explanation can play to Gigenerenzer et al.'s “ecological” analysis of why heuristics succeed.

Studies have shown that as MRI T2 relaxation time lengthens there is a shift toward more unbound or “free-water” and less partitioning of the protein/lipid molecules per unit volume. A shift toward less water partitioning or lengthened MRI T2 relaxation time is linearly related to reduced high frequency EEG amplitude, reduced short distance EEG coherence, increased long distance EEG coherence, and reduced cognitive functioning (Thatcher et al. 1998a; 1998b).

Nevin & Grace (N&G) buttress their metaphor with some good props. However, it is still not clear what momentum is analogous to. If momentum is a measure of strength, then the authors should say so and tell us how to calculate it. Furthermore, if “other” behavior can be introduced into the equation (and N&G's foray into the applied world suggests that it can), it is unclear when the masses are accrued and how much is accrued to each behavior.

Heuristics make decisions not only fast and frugally, but often nearly as well as “full” rationality or even better. Using such heuristics should therefore meet health care standards under liability law. But an independent court often has little chance to verify the necessary information. And judgments based on heuristics might appear to have little legitimacy, given the widespread belief in formal rationality.

The target article provides a useful investigative model for studying social behaviors, but it falls short of establishing a more comprehensive conceptual framework for understanding complex social inter- actions. Social behaviors such as play involve a dynamic and complex interplay between two or more organisms. Even when feed-forward mechanisms are taken into account and the model is anchored to evolutionary theory, the utility of this model is still limited by the conspicuous absence of neurobiological theory and data.

Metaphors, particularly the implicit ones, constrain imagination. If we think of the brain as a collection of centers of cognitive activations, lighting up on demand, then this becomes all we can imagine. By thinking of the cortex as propagating its functional work through physical waves, Nunez offers us a new, rich model for distributed representation. Now let's add real anatomy.

Patterns of dream content indicating a predominance of themes relating to threat are likely to reflect biases in dream recall and dream scoring techniques. Even if this pattern is not artifactual, it is yet reflective of threat-related biases in our conscious and nonconscious waking cognition, and is not special to dreams.

[Revonsuo]

Different sciences approach the brain-behaviour system at various levels, but often apparently share terminology. “Function” is used both ontogenetically and phylogenetically. Within the ontogeny it has various meanings; the one adopted by Arbib et al. is that of mainstream cognitive psychology. This usage is relatively imprecise, and the psychologists who are sceptical about the ability of cognitive psychology to predict behavioural outcomes may have the same reservations about Arbib et al.'s cognitive neuroscience.

Although the momentum metaphor is successful in many ways, there remain problems with the adequacy of the notion of a force in the behavioral sense and the question of whether the conditions used to apply force can truly be separated from the conditions that establish and maintain behavioral mass.