Quartz & Sejnowski's target article concentrates on the development of a number of neural parameters, especially neuronal processes, in the mammalian brain. Data on learning-related changes in spines and synapses in the developing avian brain are consistent with a constructivist interpretation. The issue of an integration of selectionist and constructivist views is discussed.

Injury to the central or peripheral nervous system is often associated with persistent pain. After ischemic injury to the spinal cord, rats develop severe mechanical allodynia-like symptoms, expressed as a pain-like response to innocuous stimuli. In its short-lasting phase the allodynia can be relieved with the γ-aminobutyric acid (GABA)-B receptor agonist baclofen, which also reverses the hyperexcitability of dorsal horn interneurons to mechanical stimuli. Furthermore, there is a reduction in GABA immunoreactivity in the dorsal horn of allodynic rats. Clinical neuropathic pain of peripheral and central origin often cannot be relieved by opiates at doses that do not cause side effects. The loss of sensitivity to opiates may be associated with the up-regulation of endogenous antiopioid substances, such as the neuropeptide cholecystokinin (CCK). CCK and its receptor (CCK-R) protein is normally not detectable in rat dorsal root ganglion cells. After peripheral nerve section, both CCK and CCK-R are up-regulated in the dorsal root ganglia. Furthermore, CI 988, an antagonist of the CCK-B receptor, chronically coadministered with morphine, reduces autotomy, a behavior that may be a sign of neuropathic pain following peripheral nerve section. Thus, opiate insensitivity may be due to the release of CCK from injured primary afferents. Similarly, in the chronic phase of the spinal ischemic model of central pain, the allodynia-like symptom is not relieved by systemic morphine, but is significantly reversed by the CCK-B antagonist. Consequently, up-regulation of CCK and CCK-R in the CNS may also underlie opiate drug insensitivity following CNS injury. Thus, dysfunction of central inhibition involving GABA and endogenous opioids may be a factor underlying the development of sensory abnormalities and/or pain following injury to neural tissue.

(1) Non-projectable properties as opposed to the clamping of projectable properties play a primary role in triggering and guiding human action. (2) Embodiment in language-mediated memories should be qualified: (a) Language imposes a radical discretization on body constraints (second-order embodiment). (b) Metaphors rely on second-order embodiment. (c) Language users sometimes suspend embodiment.

Saunders and van Brakel question whether the special status of red, green, yellow, and blue in our perceptual organization is anything more than a shadow cast by the English language. I suggest that it is more than this. We can hardly imagine treating lime, purple, orange, and teal as unique hues, and the reason does not lie in special training. To settle the issue, I suggest some lines for psychological experiment and anthropological investigation.

Quartz & Sejnowski's (Q&S's) constructivist manifesto promotes a return to an extreme form of empiricism. In defense of learning by selection, we argue that at the neurobiological level all the data presented by Q&S in support of their constructive model are in fact compatible with a model comprising multiple overlapping stages of synaptic overproduction and selection. We briefly review developmental studies at the behavioral level in humans providing evidence in favor of a selectionist view of development.

This commentary connects some of Glenberg's ideas to similar ideas from artificial intelligence. Second, it briefly discusses hidden assumptions relating to meaning, representations, and projectable properties. Finally, questions about mechanisms, mental imagery, and conceptualization in animals are posed.

At the close of their searching critique, Saunders & van Brakel raise, but do not address, the question: “Whither colour research?” There are two distinct traditions of colour research, one based on disembodied coloured lights and another on surface colour. The coherence and integrity of both these traditions are challenged by the nonautonomy of colour.

The target article discusses various aspects of the relationship between the sympathetic system and pain. To this end, the patients under study are divided into three groups. In the first group, called “reflex sympathetic dystrophy” (RSD), the syndrome can be characterized by a triad of autonomic, motor, and sensory symptoms, which occur in a distally generalized distribution. The pain is typically felt deeply and diffusely, has an orthostatic component, and is suppressed by the ischemia test. Under those circumstances, the pain is likely to respond to sympatholytic interventions. In a second group, called “sympathetically maintained pain” (SMP) syndrome, the principal symptoms are spontaneous pain, which is felt superficially and has no orthostatic component, and allodynia. These symptoms, typically confined to the zone of a lesioned nerve, may also be relieved by sympathetic blocks. Since the characteristics of the pain differ between RSD and SMP, the underlying kind of sympathetic–sensory coupling may also vary between these cases. A very small third group of patients exhibits symptoms of both RSD and SMP. The dependence or independence of pain on sympathetic function reported in most published studies seems to be questionable because the degree of technical success of the block remains uncertain. Therefore, pain should not be reported as sympathetic function independent until the criteria for a complete sympathetic block have been established and satisfied.

Corresponding to Glenberg's distinction between the automatic and effortful modes of memory, I propose a distinction between cued and detached mental representations. A cued representation stands for something that is present in the external situation of the representing organism, while a detached representation stands for objects or events that are not present in the current situation. This distinction is important for understanding the role of memory in different cognitive functions like planning and pretense.

Saunders & van Brakel argue, inter alia, that there is “little evidence” for the claim that there are four unique hues (red, green, blue, and yellow), and that there are two corresponding opponent processes. We argue that this is quite mistaken.

Dysfunction or injury of pain-transmitting primary afferents' central pathways can result in pain. The organism as a whole responds to such injury and consequently many symptoms of neuropathic pain develop. The nervous system responds to painful events and injury with neuroplasticity. Both peripheral sensitization and central sensitization take place and are mediated by a number of biochemical factors, including genes and receptors. Correction of altered receptors activity is the logical way to intervene therapeutically. [berkley; blumberg et al.; coderre & katz; dickenson; mcmahon; wiesenfeld-hallinet al.]

Quartz & Sejnowski (Q&S) disregard evidence that suggests that their view of dendrites is inadequate and they ignore recent results concerning the role of neurotrophic factors in synaptic remodelling. They misrepresent neuronal selectionism and thus erect a straw-man argument. Finally, the results discussed in section 4.2 require neuronal proliferation, but this does not occur during the period of neuronal development of relevance here.

Developmental psychology should play an essential constraining role in developmental cognitive neuroscience. Theories of neural development must account explicitly for the early emergence of knowledge and abilities in infants and young children documented in developmental research. Especially in need of explanation at the neural level is the early emergence of meta-representation.

Researchers in the field of discourse processing have investigated how mental models are constructed when adults comprehend stories. They have explored the process of encoding various classes of inferences “on-line” when these mental microworlds are constructed during comprehension. This commentary addresses the extent to which these inferences and mental microworlds are “embodied.”

The question of whether colour categorisation is determined by nontrivial constraints (i.e., universal neurophysiological properties of visual neurons) is an empirical issue concerning the organisation of the internal colour space. Rosch has provided psychological evidence that categories are organised around focal colours and that the organisation is universal; this commentary reconsiders that evidence.

Complex regional pain syndromes (reflex sympathetic dystrophy, causalgia) are often characterized by pain and autonomic and motor abnormalities. Pathophysiological mechanisms are in the central and peripheral nervous system. Differences in skin temperature and “the ischemia test” may be used as diagnostic criteria. Sympathetic blocks relieve pain and other symptoms in a subgroup of patients (sympathetically maintained pain, SMP). [blumberg et al.]

Both the sensory and the motivational-affective component of pain must be taken into account in studies on sex differences as well as on neuropathic, postoperative, sympathetic, and visceral pain. In all these cases, therapeutic strategies should be aimed at controlling the peripheral, central, and psychological mechanisms underlying the global pain experience. Similarly, it should be recalled that some neuropeptides act on both sensory and affective pain mechanisms. [berkley; mcmahon; dickenson; coderre & katz; wiesenfeld-hallin et al.; blumberg et al.]

We acknowledge that empirical support for universal colour categories in colour cognition is insufficient: it relies too heavily on Rosch-Heider's work with the Dani. We offer new evidence supporting universal perceptual-cognitive colour categories. The same data also support language modulating colour-cognition: Universal structures are fine-tuned by language.

Glenberg argues for embodied representations relevant to action. In contrast, we propose a grouping of representations, not necessarily all being directly embodied. Without assuming the existence of representations that are not directly embodied, one cannot account for the use of knowledge abstracted from direct experience.

The radical empiricist theory of the Quartz & Sejnowski target article would result in a brain that could not act. The attempt to bolster this position with computational arguments is misleading and often just wrong. Fortunately, other efforts are making progress in linking neural and cognitive development.