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PubMed2006

Absolute pitch among American and Chinese conservatory students: prevalence differences, and evidence for a speech-related critical period.

Absolute pitch is extremely rare in the U.S. and Europe; this rarity has so far been unexplained. This paper reports a substantial difference in the prevalence of absolute pitch in two normal populations, in a large-scale study employing an on-site test, without self-selection from within the target populations. Music conservatory students in the U.S. and China were tested. The Chinese subjects spoke the tone language Mandarin, in which pitch is involved in conveying the meaning of words. The American subjects were nontone language speakers. The earlier the age of onset of musical training, the greater the prevalence of absolute pitch; however, its prevalence was far greater among the Chinese than the U.S. students for each level of age of onset of musical training. The findings suggest that the potential for acquiring absolute pitch may be universal, and may be realized by enabling infants to associate pitches with verbal labels during the critical period for acquisition of features of their native language.

Adolescent↗
PubMed1991

Visual-evoked response binocular summation in normal and strabismic infants. Defining the critical period.

Pattern visual-evoked response binocular summation (VERBS) was recorded in normal infants, between the ages of 1-58 months, and in similar-aged esotropic infants before and at various times after corrective surgery. The normal subjects had no significant VERBS at 1.5 months of age, developed a rapid acceleration of VERBS between 1.5-3 months, and then gradually declined in VERBS from 3-58 months. The peak of the VERBS by age function at 3 months was well in the facilitation range (greater than 2.0) and corresponded to the general age range for the onset of binocular eye alignment, fusion, and stereopsis. The results from the early-onset esotropic patients revealed a similar function to that found in normal subjects; however, the function was triggered by surgical eye alignment. The peak of the VERBS function for esotropic subjects was lower than normal, and the initial rise was less rapid. It is proposed that the VERBS function reflects the human critical period for the development of binocular vision. In this framework, data from both infant developmental studies and adult studies were clarified.

Adolescent↗
PubMed2006

Hormone therapy and cognitive function: is there a critical period for benefit?

The large majority of women receiving hormone therapy initiate therapy early in life for the treatment of menopausal symptoms. However, the Women's Health Initiative Memory Study, the only randomized clinical trial to date on hormone therapy and dementia, was carried out in women age 65 and older. That trial provided important insights into the detrimental effects of hormone therapy on dementia in women initiating later in life. The generalizability of those findings to the typical hormone therapy user who initiates earlier in life is unknown. To address this important issue, this review focuses on observational trials of hormone therapy and dementia risk, randomized clinical trials of hormone therapy and cognitive function, and basic science studies. These lines of research provide suggestive, but not definitive, evidence that early initiation of hormone therapy may provide cognitive benefits, particularly to verbal memory and other hippocampally mediated functions. Other forms of hormone therapy, other cognitive domains, and cyclic hormone regimens may not conform to this "critical period hypothesis." Further research is needed to test the validity and limits of this hypothesis.

Clinical Trials as Topic↗
PubMed2002

Nicotine exposure during a postnatal critical period alters NR2A and NR2B mRNA expression in rat auditory forebrain.

Chronic nicotine exposure (CNE) can alter brain development and is thought to produce deficits in auditory function. Previously, we found that CNE during the second postnatal week, but not before or after, increases the duration of excitatory postsynaptic potentials (EPSPs) mediated by N-methyl-D-aspartate receptors (NMDARs) in rat auditory cortex. It was proposed that a potential mechanism underlying increased EPSP duration could be over-stimulation of presynaptic nicotinic acetylcholine receptors, leading to prolonged glutamate release. Since glutamatergic activity regulates levels of postsynaptic NMDAR subunits, here we examine the effects of CNE on mRNA expression for the NR2A and NR2B subunits in auditory cortex and thalamus. Two days of CNE (postnatal days 8-9), produced no effects, but 5 days (postnatal days 8-12) enhanced cortical NR2A mRNA levels and reduced thalamic NR2B mRNA levels for up to 2 weeks. These effects are consistent with the hypothesis that CNE during a postnatal critical period disrupts auditory cortex development by over-stimulating glutamatergic synapses.

Aging↗
PubMed2002

Disruption of primary auditory cortex by synchronous auditory inputs during a critical period.

In the primary auditory cortex (AI), the development of tone frequency selectivity and tonotopic organization is influenced by patterns of neural activity. Introduction of synchronous inputs into the auditory pathway achieved by exposing rat pups to pulsed white noise at a moderate intensity during P9-P28 resulted in a disrupted tonotopicity and degraded frequency-response selectivity for neurons in the adult AI. The latter was manifested by broader-than-normal tuning curves, multipeaks, and discontinuous, tone-evoked responses within AI-receptive fields. These effects correlated with the severe impairment of normal, developmental sharpening, and refinement of receptive fields and tonotopicity. In addition, paradoxically weaker than normal temporal correlations between the discharges of nearby AI neurons were recorded in exposed rats. In contrast, noise exposure of rats older than P30 did not cause significant change of auditory cortical maps. Thus, patterned auditory inputs appear to play a crucial role in shaping neuronal processing/decoding circuits in the primary auditory cortex during a critical period.

Age Factors↗
PubMed1996

Non-uniform distribution of the NMDAR1 receptor subunit in kitten visual cortex at the peak of the critical period.

PURPOSE: The development of columnar systems in the visual cortex, in particular ocular dominance columns, is dependent on experiential activity in conjunction with NMDA-mediated plasticity mechanisms. Recent experiments, however, have shown that certain aspects of the columnar organization of the visual cortex, such as the spacing of columns, are not changed by manipulations that affect the pattern of retinal activity. This raises the possibility that features intrinsic to the visual cortex may play a crucial role in the development of cortical columns and that a non-uniform distribution of NMDA receptors in the developing visual cortex could form the link between activity and intrinsic cortical modularity. METHODS: To examine this possibility we used immunohistochemical techniques to label the NMDAR1 receptor subunit protein in kitten visual cortex. The arrangement of the NMDAR1 subunit was visualized (using a monoclonal antibody) in flattened and coronal sections through visual cortex. The tangential and laminar distributions of NMDAR1 immunoreactivity (NMDAR1ir) were studied at the peak of the critical period for plasticity (4-5 weeks of age) in the developing kitten visual cortex. RESULTS: At the ages examined there was a non-uniform distribution of NMDAR1 immunoreactivity in the visual cortex. These patches of darker NMDAR1 label were found in layers 2/3 and extended up into layer 1. Thus, during development neurons expressing the NMDAR1 receptor subunit were distributed in a patchy fashion in the upper layers of the kitten visual cortex. CONCLUSIONS: This suggests that NMDA-mediated activity-dependent plasticity may not occur uniformly across the tangential extent of the visual cortex, and raises the possibility that the arrangement of NMDAR1 patches may guide the emergence of nascent columns in the developing visual cortex.

Animals↗
PubMed1992

Critical period for monocular deprivation in the cat visual cortex.

1. Cats were monocularly deprived for 3 mo starting at 8-9 mo, 12 mo, 15 mo, and several years of age. Single cells were recorded in both visual cortexes of each cat, and the ocular dominance and layer determined for each cell. Ocular dominance histograms were then constructed for layers II/III, IV, and V/VI for each group of animals. 2. There was a statistically significant shift in the ocular dominance for cells in layers II/III and V/VI for the animals deprived between 8-9 and 11-12 mo of age. There was a small but not statistically significant shift for cells in layer IV from the animals deprived between 8-9 and 11-12 mo of age, and for cells in layers V/VI from the animals deprived between 15 and 18 mo of age. There was no noticeable shift in ocular dominance for any other layers in any other group of animals. 3. We conclude that the critical period for monocular deprivation is finally over at approximately 1 yr of age for extragranular layers (layers II, III, V, and VI) in visual cortex of the cat.

Aging↗
PubMed1994

Requirement of a critical period of transcription for induction of a late phase of LTP.

Repeated high-frequency trains of stimuli induce long-term potentiation (LTP) in the CA1 region that persists for up to 8 hours in hippocampal slices and for days in intact animals. This long time course has made LTP an attractive model for certain forms of long-term memory in the mammalian brain. A hallmark of long-term memory in the intact animal is a requirement for transcription, and thus whether the late phase of LTP (L-LTP) requires transcription was investigated here. With the use of different inhibitors, it was found in rat hippocampal slices that the induction of L-LTP [produced either by tetanic stimulation or by application of the cyclic adenosine monophosphate (cAMP) analog Sp-cAMPS (Sp-cyclic adenosine 3',5'-monophosphorothioate)] was selectively prevented when transcription was blocked immediately after tetanization or during application of cAMP. As with behavioral memory, this requirement for transcription had a critical time window. Thus, the late phase of LTP in the CA1 region requires transcription during a critical period, perhaps because cAMP-inducible genes must be expressed during this period.

Animals↗
PubMed1991

Latency and temporal overlap of visually elicited contralateral and ipsilateral firing in Xenopus tectum during and after the critical period.

The mechanisms underlying the development of proper topographic registration of binocular maps in the tectum of Xenopus laevis involve correlation of activity patterns of ipsilateral and contralateral inputs. Recent evidence implicates NMDA-type glutamate receptors in this process. In general, NMDA receptors are considered to function optimally when there are multiple, simultaneous excitatory inputs to a dendrite. In the binocular system of the frog, however, the ipsilateral eye's response to a visual stimulus reaches the tectum later than the contralateral eye's response. The reason for this delay is that the ipsilateral pathway to the tectum is indirect, involving a relay in the opposite tectum and nucleus isthmi. In this paper, we evaluate the duration of the delay between arrival of contralateral and ipsilateral input in response to cessation of light and we also gauge the extent of temporal overlap in responses of the two inputs. We find that the average delay is about 10 ms and that this delay is not significantly different during the critical period vs later in development. The temporal overlap is 40-60 ms in duration. We conclude that the intertectal delay does not prevent a substantial period of simultaneous firing of ipsilateral and contralateral inputs in response to sudden changes in illumination. Therefore, the firing patterns of these afferents are compatible with a mechanism of activity-dependent alignment of binocular maps in the tectum.

Animals↗
PubMed1988

A critical period for formation of secondary myotubes defined by prenatal undernourishment in rats.

Rats fed a restricted diet during gestation and lactation gave birth to pups with about 60% the normal birthweight. Maintaining the undernutrition after birth reduced the rate of growth of the pups so that their body weights were only 40% of control at PN7. Soleus and lumbrical muscles in these animals had reduced numbers of muscle fibres, and quantitative examination of embryonic muscles revealed that this was due solely to a decreased formation of secondary myotubes; the number of primary myotubes remained normal. Undernutrition did not affect the number of motoneurones surviving normal developmental death. Restoration of normal dietary intake on E21, one day before birth, did not correct the deficit in muscle fibre numbers in soleus muscles examined when the animals reached one month of age. Development of the lumbrical muscle lags behind the soleus and unrestricted feeding from E21 onwards allowed a normal number of fibres to develop from this time on, although the initial deficit was never restored. These experiments define a critical period in muscle development during which the potential maximum number of secondary myotubes is determined.

Animals↗
PubMed2001

Estradiol and para-chlorophenylalanine downregulate the expression of brain aromatase and estrogen receptor-alpha mRNA during the critical period of feminization in tilapia (Oreochromis mossambicus).

The period of maximal feminizing action of 17beta-estradiol (E(2)) upon sex ratio is before 10 days posthatching in tilapia (Oreochromis mossambicus). The effect of E(2) at this time is mimicked by para-chlorophenylalanine (p-CPA), a serotonin (5-hydroxytryptamine; 5-HT) synthesis inhibitor. The effect of E(2) on sexual differentiation may be mediated by the 5-HT system, which is consistent with the suggestion in mammals. The masculinizing actions of 17alpha-methyltestosterone (MT) are most potent later at up to day 20 of age, and may depend on MT induction of aromatase activity. In the present study, the effects of gonadal steroids and p-CPA on brain aromatase and estrogen receptor (ER) mRNA expression during the critical period of sexual differentiation were investigated. Treatment of tilapia with E(2) resulted in a significant decrease in the expression of brain aromatase and ERalpha between days 0 and 10, but not subsequently. The effect of E(2) at this time can be mimicked by p-CPA. Treatment of tilapia with MT, by contrast, resulted in a significant increase in brain aromatase, ERalpha and ERbeta mRNA expression when given between days 10 and 20. The downregulation of brain aromatase and ERalpha mRNA expression by E(2) before 10 days of age and, in turn, the upregulation of brain aromatase and ERalpha and ERbeta mRNA expression by MT at up to day 20 of age coincide with the period in which E(2) and MT have the maximal effect on gonadal feminization and masculinization, respectively.

Actins↗
PubMed2004

Experience and activity-dependent maturation of perisomatic GABAergic innervation in primary visual cortex during a postnatal critical period.

The neocortical GABAergic network consists of diverse interneuron cell types that display distinct physiological properties and target their innervations to subcellular compartments of principal neurons. Inhibition directed toward the soma and proximal dendrites is crucial in regulating the output of pyramidal neurons, but the development of perisomatic innervation is poorly understood because of the lack of specific synaptic markers. In the primary visual cortex, for example, it is unknown whether, and to what extent, the formation and maturation of perisomatic synapses are intrinsic to cortical circuits or are regulated by sensory experience. Using bacterial artificial chromosome transgenic mice that label a defined class of perisomatic synapses with green fluorescent protein, here we show that perisomatic innervation developed during a protracted postnatal period after eye opening. Maturation of perisomatic innervation was significantly retarded by visual deprivation during the third, but not the fifth, postnatal week, implicating an important role for sensory input. To examine the role of cortical intrinsic mechanisms, we developed a method to visualize perisomatic synapses from single basket interneurons in cortical organotypic cultures. Characteristic perisomatic synapses formed through a stereotyped process, involving the extension of distinct terminal branches and proliferation of perisomatic boutons. Neuronal spiking in organotypic cultures was necessary for the proliferation of boutons and the extension, but not the maintenance, of terminal branches. Together, our results suggest that although the formation of perisomatic synapses is intrinsic to the cortex, visual experience can influence the maturation and pattern of perisomatic innervation during a postnatal critical period by modulating the level of neural activity within cortical circuits.

Action Potentials↗
PubMed2002

Experience-dependent plasticity of zinc-containing cortical circuits during a critical period of postnatal development.

Distinctive subsets of glutamatergic neurons in cerebral cortex sequester the transition metal zinc within the synaptic vesicles of their axon terminals. In the present study we used histochemical localization of synaptic zinc to investigate normal postnatal development and experience-dependent plasticity of zinc-containing circuits in somatosensory barrel cortex of rats. First, we found that zinc-containing cortical circuits are dynamically reorganized between postnatal day (P) 0 and P28. Whereas most cortical laminae exhibited idiosyncratic increases in zinc histochemical staining with advancing age, lamina IV barrels were darkly reactive early in life and then lost much of their complement of synaptic zinc during postnatal weeks 2-4. Second, we established that sensory experience plays a major role in sculpting the zinc-containing innervation of cortical barrels. Trimming a particular facial whisker arrested the normal postnatal decline in synaptic zinc in the corresponding, deprived barrel. This resulted in more intense zinc staining in deprived barrels compared with adjacent, nondeprived barrels. Notably, the influence of experience on development of zinc circuits was most robust during a critical period extending from about P14, when an effect of whisker trimming first could be observed, through P28, after which time chronic deprivation no longer resulted in heightened levels of synaptic zinc in lamina IV. These findings indicate that sensory input can have a marked influence on development of cortical circuits, including those within lamina IV, throughout the first postnatal month.

Afferent Pathways↗
PubMed1992

[The critical period in natural fertility].

In order to learn the natural expectancy period of first pregnancy as well as the influences of some biosocial variables, a clinical-retrospective study was performed within 1120 gravida I women. All of them attended the major institutes of health care in Mexico City (IMSS, ISSSTE, SS and DDF). Data were obtained by means of predetermined questions from subjects after the first postpartum hours. None of them had previously used any contraceptive method. Results showed age at the first pregnancy: 21.6 +/- 3.8 (years); gestational interval 22.1 +/- 19.9 (months) and a 67% achievement rate the following twelve months of sexual activity. Eutocia was seen in 54% of these population and significant linear correlation was attained between age of the patient and the gestational interval. It seems that this is the first information regarding the fertility critical period within our society.

Adolescent↗
PubMed1995

Monocular visual deprivation at the critical period modulates photic evoked responses.

Photic evoked responses were recorded from the striate cortex of Long-Evans hooded normal (control) rats and from monocular visual deprivation (MD) rats. The averaged visual evoked responses (AVER) were obtained from both hemispheres and provide comparison between the contralateral and the ipsilateral striate cortex with relation to the monocular deprived eye. The AVER recorded following binocular photic stimulation after 1 month of monocular deprivation demonstrated that the two visual cortexes responded differently. In the contralateral hemisphere of the visual cortex (related to the MD eye), all three components (P2, N2 and P3) of the AVER of the MD rats had significant increases in their peak amplitude as compared to the control recordings. In the ipsilateral cortex, the amplitude of component P2 and N2 was significantly reduced as a result of 1 month of MD. Comparing the AVER amplitudes of the two homotopic sites of the visual cortex obtained from the control group reveals no differences between the two hemispheres but markedly significant differences in P2, N2 and P3 components for the MD group. Based on the literature, the possibility that the monocular visual deprivation at the critical period in early developmental stage modulates the AVER as a result from the neurocytological alteration from altering of GABA and ACh within the striate cortex was discussed. In conclusion, the AVER is a reliable and practical method for studying the effects of monocular deprivation and neuroplasticity in the rat visual cortex.

Animals↗
PubMed2002

Critical period for cross-modal plasticity in blind humans: a functional MRI study.

The primary visual cortex (V1) in congenitally blind humans has been shown to be involved in tactile discrimination tasks, indicating that there is a shift in function of this area of cortex, but the age dependency of the reorganization is not fully known. To investigate the reorganized network, we measured the change of regional cerebral blood flow using 3.0 Tesla functional MRI during passive tactile tasks performed by 15 blind and 8 sighted subjects. There was increased activity in the postcentral gyrus to posterior parietal cortex and decreased activity in the secondary somatosensory area in blind compared with sighted subjects during a tactile discrimination task. This suggests that there is a greater demand for shape discrimination processing in blind subjects. Blind subjects, irrespective of the age at onset of blindness, exhibited higher activity in the visual association cortex than did sighted subjects. V1 was activated in blind subjects who lost their sight before 16 years of age, whereas it was suppressed in blind subjects who lost their sight after 16 years of age during a tactile discrimination task. This suggests that the first 16 years of life represent a critical period for a functional shift of V1 from processing visual stimuli to processing tactile stimuli. Because of the age-dependency, V1 is unlikely to be the "entry node" of the cortex for the redirection of tactile signals into visual cortices after blinding. Instead, the visual association cortex may mediate the circuitry by which V1 is activated during tactile stimulation.

Adult↗
PubMed1980

A critical period of ecdysterone action on sensitive clones of Drosophila cultured in vitro: the maturation of the cells.

Ecdysterone-sensitive clones cultured in vitro were isolated from established cell lines of Drosophila melanogaster. The clones FC and 89K are ecdysterone-inducible for two enzymatic activities: acetylcholinesterase and beta-galactosidase. No activity could be detected in untreated cells, whereas after treatment with 50-250 nM ecdysterone, the activity appeared after one day and increased during 3-4 days. We wanted to modulate the response of the cells by varying the conditions of the hormonal stimulus. Mimicking the physiological situation of Drosophila (the ecdysterone peak corresponding to the molts is preceded by low levels) we pretreated the cells with a subthreshold concentration (1-5 nM) for 2 days and then we added the stimulating concentration of 50-250 nM ecdysterone. The enzymatic activities were then detectable within the following hours and the final level of induction was about twice the one of cells without pretreatment. Thus, the continuous presence of a subthreshold concentration of ecdysterone provokes the maturation of the cells which become able to respond to the hormonal stimulus by a quicker and higher enzymatic induction. The cellular maturation seems to be a critical period. It is altosid-sensitive. Altosid (a juvenile hormone analog) abolishes the effects of the ecdysterone-induced maturation.

Acetylcholinesterase↗
PubMed1996

Early postnatal muscle contractile activity regulates the carbonic anhydrase phenotype of proprioceptive neurons in young and mature mice: evidence for a critical period in development.

Carbonic anhydrase activity, a marker of mouse proprioceptive neurons in adult dorsal root ganglia, is first detectable in the perinatal period, increases until postnatal day 60 and remains stable in adulthood. The onset of carbonic anhydrase staining begins after the neurons have made connections with their targets suggesting that neuron-target interactions regulate carbonic anhydrase phenotype development. To examine this possibility, we first analysed carbonic anhydrase expression in mdx mice which are characterized by a massive but reversible degeneration of skeletal muscle concomitant with the carbonic anhydrase ontogenesis. Neuronal carbonic anhydrase expression in mdx mice stopped developing when the period of muscular degeneration-regeneration began. Furthermore this alteration persisted during adulthood. We then analysed carbonic anhydrase expression in fifth lumbar dorsal root ganglion of developing control mice before and after surgical procedures that might interfere with central and peripheral target influences on dorsal root ganglion neurons. Central disconnection (dorsal rhizotomy) did not affect the development of carbonic anhydrase activity. Disrupting neuron-peripheral target interactions by sciatic nerve transection or blocking muscle contraction by tenotomy stopped the development of neuronal carbonic anhydrase content. Finally, recovery was monitored following sciatic nerve crush. In adults, recovery of carbonic anhydrase activity was obtained after functional recuperation; similar manipulations during the first month of life induced irreversible alteration of the carbonic anhydrase phenotype. These results show that the development of carbonic anhydrase activity in proprioceptive neurons is regulated by neuron-muscle interactions (i.e. muscle contraction). They also provide evidence for a critical period in the development of the carbonic anhydrase phenotype. We suggest that these two mechanisms are responsible for the altered carbonic anhydrase phenotype of the dorsal root ganglion neurons in mdx mice, a model of human muscular dystrophy.

Age Factors↗