The belief that women report more somatic complaints than men is not new. Many centuries b.c., the Egyptians and the Greeks already made an association between female pains and hysteria, which is Greek for “wandering womb.” Despite the commonly held belief that women are more sensitive to pain than men, the issue of sex differences in pain has received little attention from the scientific community in general. It is the merit of berkley to draw our attention to this large gap in our scientific knowledge.

I take issue with Saunders & van Brakel's claim that neural processes play no interesting role in determining color categorizations. I distinguish an aspect of color categorization, namely, color discrimination, from other aspects. The law of trichromacy describes conditions under which physical properties cannot be discriminated in terms of color. Trichromacy is explained by properties of neural processes.

Glenberg's account falls short in several respects. Besides requiring clearer explication of basic concepts, his account fails to recognize the autonomous nature of perception. His account of what is remembered, and its description, is too static. His strictures against connectionist modeling might be overcome by combining the notions of psychological space and principled learning in an embodied and situated network.

Activity-dependent processes play an active role in shaping the structure of neuronal circuitry and therefore contribute to neural and cognitive development. Neural constructivism claims to be able to account for increases in the complexity of cognitive representations in terms of directed growth of neurons. This claim is overstated, rests on biased nterpretations of the evidence, and is based on serious misapprehensions of the nature of somatic variation and selection.

The strong correlation between the geometry of the dendritic tree and the specific function of motoneurons suggests that their synaptic contacts are established on a selective stochastic basis with the characteristic form of dendrites being the source of selection in the frog. A compromise is suggested according to which specific structures may have evolved on a selective stochastic basis and “constructive learning” could be the source of selection in the cortex.

Multidimensional scaling of subjective color differences has shown that color stimuli are located on a hypersphere in four-dimensional space. The semantic space of color names is isomorphic with perceptual color space. A spherical four-dimensional space revealed in monkeys and fish suggests the primacy of common neuronal basis.

According to berkley's review, women have a higher risk of suffering from pain than men. If this is true, there should be more frequent and more intense activity both in the pain excitatory system and in the pain inhibitory system of women than of men. Consequently, it remains unclear whether the overall effect at the end is more pain or less pain in women. This conclusion fits the weak sex differences observed for experimental and clinical pain as shown by berkley's review of the literature.

I address the commentators' calls for clarification of theoretical terms, discussion of similarities to other proposals, and extension of the ideas. In doing so, I keep the focus on the purpose of memory: enabling the organism to make sense of its environment so that it can take action appropriate to constraints resulting from the physical, personal, social, and cultural situations.

Some regularities enjoy only an attenuated existence in a body of training data. These are regularities whose statistical visibility depends on some systematic recoding of the data. The space of possible recodings is, however, infinitely large – it is the space of applicable Turing machines. As a result, mappings that pivot on such attenuated regularities cannot, in general, be found by brute-force search. The class of problems that present such mappings we call the class of “type-2 problems.” Type-1 problems, by contrast, present tractable problems of search insofar as the relevant regularities can be found by sampling the input data as originally coded. Type-2 problems, we suggest, present neither rare nor pathological cases. They are rife in biologically realistic settings and in domains ranging from simple animat (simulated animal or autonomous robot) behaviors to language acquisition. Not only are such problems rife – they are standardly solved! This presents a puzzle. How, given the statistical intractability of these type-2 cases, does nature turn the trick? One answer, which we do not pursue, is to suppose that evolution gifts us with exactly the right set of recoding biases so as to reduce specific type-2 problems to (tractable) type-1 mappings. Such a heavy-duty nativism is no doubt sometimes plausible. But we believe there are other, more general mechanisms also at work. Such mechanisms provide general (not task-specific) strategies for managing problems of type-2 complexity. Several such mechanisms are investigated. At the heart of each is a fundamental ploy – namely, the maximal exploitation of states of representation already achieved by prior, simpler (type-1) learning so as to reduce the amount of subsequent computational search. Such exploitation both characterizes and helps make unitary sense of a diverse range of mechanisms. These include simple incremental learning (Elman 1993), modular connectionism (Jacobs et al. 1991), and the developmental hypothesis of “representational redescription” (Karmiloff-Smith 1979; 1992). In addition, the most distinctive features of human cognition – language and culture – may themselves be viewed as adaptations enabling this representation/computation trade-off to be pursued on an even grander scale.

Saunders & van Brakel prematurely reject the idea of nontrivial constraints in color nomenclature. Their claim that the universality of color naming is caused by Western contact and cultural dominance is inadequate because of the great variety of terminology systems still found in the world. The complex interactions of hue, brightness, and saturation can be studied rigorously. If we discard the standard models of color nomenclature because of some discrepancies and anomalies, we will not be able to explain the vast array of remaining data that is consistent with current theories.

As the commentaries reveal, cognitive neuroscience's first steps toward a theory of development are marked by vigorous debate, ranging from basic points of definition to the fine details of mechanism. In this Response, we present the neural constructivist position on this broad spectrum of issues, from basic questions such as what sets constructivism apart from other theories (particularly selectionism) to its relation to behavioral theories and to its underlying mechanisms. We conclude that the real value of global theories at this stage of cognitive neuroscience is not just their answers but the new set of research questions they pose.

Abundant pathophysiological and clinical evidence suggests that the algogenic code responsible for cardiac pain is not based on “specific” mechanisms (mcmahon). Recent evidence, however, has led various authors to postulate that some degree of specificity might be involved in visceral pain arising from other sources, but a “spatio-temporal” intensity pattern is still the most plausible hypothesis for the genesis of visceral pain.

Despite close scrutiny in recent years, the traditional properties of LTP are holding up remarkably well, and they remain a credible influence on the belief that LTP has something to do with learning and information storage.

Clark & Thornton are too hasty in their dismissal of uninformed learning; nonmonotonic processing units show considerable promise on type-2 tasks. I describe a simulation which succeeds on a “pure” type-2 problem. Another simulation challenges Clark & Thornton's claims about the serendipitous nature of solutions to type-2 problems.

Confusion concerning the issue of universality of colour categorization would greatly diminish if context regains its fundamental status in psychological research and we give up on the reductionist notion that biological universality implies behavioral universality.

My commentary on mcmahon addresses the fact that only peripheral data have been considered for explaining differential sensibility in somato- and viscerosensory systems. This fails to take it into account that central processing for visceral and somatic inputs is now known to depend on different functional pathways. My commentary on berkley points out that the hypothalamus-pituitary axis is more responsive to stress in females than in males.

Saunders and van Brakel propose that we rethink or reject much of current colour theory. Many of the problems they cite appear to call for further research rather than a radical rethinking of colour theory. The controversy described in this target article appears to be itself a case of “ekphrasis,” or something that does not exist.

The central hyperexcitability observed in animal models supports a pathophysiological explanation for chronic human pain. Novel information on cholecystokinin (CCK) upregulation offers a rationale for reduced opioid response in neuropathic pain. However, the basic information provided by scientists should not lead clinicians to equate experimental models to chronic human conditions. Clinicians should provide careful reports and attempt to classify pathophysiologically clinical conditions that have so far been grouped generically. [blumberg et al.; coderre & katz; dickenson; wiesenfeld-hallin et al.]

Long-term potentiation (LTP) is operationally defined as a long-lasting increase in synaptic efficacy following high-frequency stimulation of afferent fibers. Since the first full description of the phenomenon in 1973, exploration of the mechanisms underlying LTP induction has been one of the most active areas of research in neuroscience. Of principal interest to those who study LTP, particularly in the mammalian hippocampus, is its presumed role in the establishment of stable memories, a role consistent with “Hebbian” descriptions of memory formation. Other characteristics of LTP, including its rapid induction, persistence, and correlation with natural brain rhythms, provide circumstantial support for this connection to memory storage. Nonetheless, there is little empirical evidence that directly links LTP to the storage of memories. In this target article we review a range of cellular and behavioral characteristics of LTP and evaluate whether they are consistent with the purported role of hippocampal LTP in memory formation. We suggest that much of the present focus on LTP reflects a preconception that LTP is a learning mechanism, although the empirical evidence often suggests that LTP is unsuitable for such a role. As an alternative to serving as a memory storage device, we propose that LTP may serve as a neural equivalent to an arousal or attention device in the brain. Accordingly, LTP may increase in a nonspecific way the effective salience of discrete external stimuli and may thereby facilitate the induction of memories at distant synapses. Other hypotheses regarding the functional utility of this intensely studied mechanism are conceivable; the intent of this target article is not to promote a single hypothesis but rather to stimulate discussion about the neural mechanisms underlying memory storage and to appraise whether LTP can be considered a viable candidate for such a mechanism.

I suggest that the difficulties inherent in discovering the hidden regularities in realistic (type-2) problems can often be resolved by learning algorithms employing simple constraints (such as symmetry and the importance of local information) that are natural from an evolutionary point of view. Neither “heavy-duty nativism” nor “representational recoding” appear to offer totally appropriate descriptions of such natural learning processes.