“Normal movements” in atypical populations address the question of postural control: Voluntary movement is a perturbation of body balance and cannot be executed without a convenient counterperturbation. Despite a change in the postural program in relation to the impairment (Parkinson's disease, paraplegia), the performance level is decreased. Movements are not “normal,” owing to a reduction in posturokinetic capacity.

Vincent proposes that the extracellular cGMP found in cerebellum after glutamate receptor activation is released mainly from Purkinje cells because in these neurons the presence of guanylate cyclase has been shown using monoclonal antibodies. It is uncertain, however, whether Purkinje cells are the only source of extracellular cGMP in the cerebellum. This commentary examines the possibility that glial and cerebellar granule cells may also participate in cGMP synthesis and release, Moreover, the hypothesis of transcellular metabolism of citrulline and arginine is discussed. [VINCENT]

The study of signed languages has inspired scientific' speculation regarding foundations of human language. Relationships between the acquisition of sign language in apes and man are discounted on logical grounds. Evidence from the differential hreakdown of sign language and manual pantomime places limits on the degree of overlap between language and nonlanguage motor systems. Evidence from functional magnetic resonance imaging reveals neural areas of convergence and divergence underlying signed and spoken languages.

Analyses of bodies of data usually omit some relevant studies. Geary omits (1) some studies looking at functional correlates of basic biological data, (2) studies of developmental implications for functioning, and (3) the recent achievement of acceleration of cognitive development.

Latash & Anson's contention that movement patterns that are different from those typically observed in persons without impairments should not be considered abnormal and usually should not be corrected is consistent with Davis & Burton's Ecological Task Analysis (ETA). Extending from the ETA concept of performer-scaled performance measures, the use of Froude numbers may offer insight into the global dynamics of a person's action system.

We criticize the synaptic theory of long-term memory and the inappropriate usage of physical notions such as “joint stiffness” in motor control theories. Motor control and motor memory hypotheses should be based on explicitly specified hypothetical control variables that are sound from both physiological and physical perspectives. [HOUK et al.; SMITH; THACH]

Müller argues that general cognitive skills and linguistic skills are not necessarily independent. However, cross-linguistic evidence from an inherited specific language disorder affecting productive rules suggests significant degrees of modularity, innateness, and universality of language. Confident claims about the overall nature of such a complex system still await more interdisciplinary research.

The target article draws on evolutionary theory to formulate a biosocial model of sex differences in quantitative abilities. Unfortunately, the data do not support some of the crucial hypotheses. The male advantage in geometry is not appreciably greater than the male advantagi in algebra, and the greater male variability in mathematics cited by Gear is not cross-culturally invariant.

Adaptive motor patterns that emerge after a neuromusculoskeletal lesion reflect not only the primary lesion, but also the dynamic characteristics of the musculoskeletal linkage and environment in which the action is performed. Although these patterns may be optimal, they may also be ineffective as goal-directed actions; effectiveness may only be regained if training addresses primary deficits and ensures practice without gross biomechanical adaptations.

We suggest that the cerebellum generates sensory or “state” estimates based on outgoing motor commands and sensory feedback. Thus, it is not a motor pattern generator (HOUK et al.) but a predictive system which is intimately involved in motor behavior. This theory may explain the sensitivity of the climbing fibers to both unexpected external events and motor errors (SIMPSON et al.), and we speculate that unusual biophysical properties of the inferior olive might allow the cerebellum to develop multiple asynchronous sensory estimates, [HOUK et al.; SIMPSON et al.; THACH]

Geary's project faces the severe methodological difficulty of tracing the biological effects of gender on mathematical ability in a system that is massively open. Two methodological stratagems he uses are considered. The first is that pancultural sex differences are biological in nature, which is dubious in the domain of mathematics, since it is completely culture-bound. The second is that sociosexual differences are partly caused by biosexual differences, which renders his thesis unfalsifiable and empirically empty.

Both autonomy and local specificity are compatible with observed interconnectivity at the cell level when considering two different levels: cell assemblies and brain systems. Early syntactic structuring processes in particular are likely to representan autonomous module in the language/brain system.

Latash & Anson argue that changed motor patterns should not be viewed as pathological. Instead, they should be viewed as adaptations to a primary deficit. We argue that the evidence shows: (1) bradykinesia is not an adaptation to a different primary deficit, and (2) bradykinetic movements are not “normal” slowed movements but, to the contrary, bradykinesia is part of the pathophysiology of Parkinson's disease.

Müller attempts to downplay cases of dissociation between language and cognition as evidence against the modularity of language. We review cases of associations between verbal and nonverbal abilities as further evidence against the notion of language as an autonomous subsystem. We also point out a discrepancy between his proposal of homologies between nonhuman primates' communication and human language and recent proposals on the evolution of language.

In addition to SNP and SIN-1, SNAP suppresses AMPA responses. This suppression is antagonized by carboxy-PTIO in cultured chick cerebellar Purkinje neurons. Intracellular application of cGMP shows a long-lasting suppression of AMPA responses mimicking the cerebellar LTD. These recent results demonstrate that NO can induce LTD-like suppression of AMPA responses and intracellular cGMP and cGMP-dependent protein kinase participate in this suppression. [CRÉPEL et al.; LINDEN; VINCENT]

We challenge the notion that differences in spatial ability are the best or only explanation for observed sex differences in mathematical word problems. We suggest two ideas from the study of autism: sex differences in theory of mind and in central coherence.

The conclusion that language is not really innate or modular is based on several fallacies. I show that the target article confuses communicative skills with linguistic abilities, and that its discussion of brain/language relations is replete with factual errors. I also criticize its attempt to contrast biological and linguistic principles. Finally, I argue that no case is made for the “alternative” approach proposed here.

The involvement of nitric oxide in cerebellar long-term depression is supported by the observation that nitric oxide is released by climbing fiber stimulation and by pharmacological tool usage. Two forms of long-term depression – one depending on large calcium increase and another on nitric oxide – should be distinguished by their physiological relevance. [CRÉPEL et al.; LINDEN; VINCENT]

We agree with Latash & Anson that therapeutic approaches should be directed toward solving the underlying problem, not toward adapting the abnormal to normal behaviour. The fundamental obstacle, however, is that doing so requires a solution of the “equivalence problem” in movement control.

In Darwinian terminology, “sexual selection” refers to purely reproductive competition and is conceptually distinct from natural selection as it affects reproduction generally. As natural selection may favor the evolution of sexual dimorphism by virtue of the division of labor between males and females, this possibility needs to be taken very seriously.