Adult-like Levels Research Articles

Preschool children's ability to visually represent relations

The developmental origins of mapping temporal relations onto space was investigated in N = 122 3- to 5-year-old children and adults. Spontaneous production and comprehension were investigated. Production was investigated in two conditions: an iconic condition (three-dimensional objects depicting the events or objects to be represented) and an abstract condition (plain discs). Consistent with findings by Tversky, Kugelmass and Winter (1991), 5-year-olds performed on an adult-like level. Developmental progress was observed between the ages of 3 and 4 years, with comprehension preceding production. Consistent with DeLoache's findings (2000), 4-year-olds' performance was better in abstract than in iconic conditions, indicating that dual representational demands may have affected task performance in the iconic condition. In sum, abilities to map temporal relations onto spatial relations appear to develop spontaneously, even before children have experience with conventional notational systems.

Developmental change in the acuity of the "number sense": The approximate number system in 3-, 4-, 5-, and 6-year-olds and adults.

Behavioral, neuropsychological, and brain imaging research points to a dedicated system for processing number that is shared across development and across species. This foundational Approximate Number System (ANS) operates over multiple modalities, forming representations of the number of objects, sounds, or events in a scene. This system is imprecise and hence differs from exact counting. Evidence suggests that the resolution of the ANS, as specified by a Weber fraction, increases with age such that adults can discriminate numerosities that infants cannot. However, the Weber fraction has yet to be determined for participants of any age between 9 months and adulthood, leaving its developmental trajectory unclear. Here we identify the Weber fraction of the ANS in 3-, 4-, 5-, and 6-year-old children and in adults. We show that the resolution of this system continues to increase throughout childhood, with adultlike levels of acuity attained surprisingly late in development.

Sex differences in the effect of prepubertal GALP infusion on growth, metabolism and LH secretion

The hypothalamic neuropeptide, galanin-like peptide (GALP), is known to have an effect on energy expenditure and reproduction in adult male rats, but little work has been done on prepubertal rats. We hypothesized that hypothalamic GALP is involved in physiological changes associated with the onset of puberty. To test this hypothesis, we first determined the postnatal ontogeny of GALP gene expression via in situ hybridization of developing male and female rat pups through adulthood. GALP gene expression was not observed in either male or female rat pups until after postnatal day (PND) 10 and did not reach adult-like levels until after weaning (PND25). To determine if exogenous GALP could induce the onset of puberty, PND25 male and female rats were implanted with lateral ventricular cannulas connected to an osmotic minipump that delivered either GALP or vehicle. GALP infusion significantly ( p < 0.05) increased body weight, food intake, and metabolic rate in male but not female rats compared to control infusion. After 2 weeks, GALP infusion had no significant effect on the onset of puberty, percent body fat, nor plasma levels of insulin, FSH or gonadal steroids in either sex; however, GALP did significantly ( p < 0.05) increase plasma levels of LH and leptin in male but not female rats and increased plasma growth hormone (GH) in both sexes. Our observations further demonstrate a sex difference in GALP responsiveness in prepubertal rats. These data suggest that GALP may be involved with the prepubertal increase in circulating leptin, LH, and GH resulting in an increase in metabolic rate and lean growth associated with puberty.

Adolescent vs. adult-onset nicotine self-administration in male rats: Duration of effect and differential nicotinic receptor correlates

Adolescence is the life stage when tobacco addiction typically begins. Adolescent neurobehavioral development may be altered by nicotine self-administration in a way that persistently potentiates addiction. Previously, we showed that female adolescent rats self-administer more nicotine than do adults and that the increased nicotine intake then persists through the transition to adulthood [E.D. Levin, A. Rezvani, D. Montoya, J. Rose, H. Swartzwelder, Adolescent-onset nicotine self-administration modeled in female rats, Psychopharmacology 169 (2003) 141–149.]. In the current study, male Sprague–Dawley rats were given access to nicotine via the standard operant IV self-administration procedure (nicotine bitartrate dose of 0.03 mg/kg/infusion). One group of male rats started during adolescence the other group started in young adulthood. After the end of the four-week period of self-administration brain regions of the rats were assessed for α4β2 nicotinic receptor binding. We found that male rats, like females, show higher nicotine self-administration when starting during adolescence as compared to starting in adulthood ( p < 0.001). Indeed, the effect in adolescent males was even greater than that in females, with more than triple the rate of nicotine self-administration vs. the adult-onset group during the first 2 weeks. The adolescent onset nicotine-self-administering rats also had significantly greater high affinity nicotinic receptor binding in the midbrain and the striatum, whereas hippocampal binding did not differ between the age groups. Striatal values significantly correlated with nicotine self-administration during the first 2 weeks in the adult-onset group but not the adolescent-onset rats, suggesting that the differences in self-administration may depend in part on underlying disparities in synaptic responses to nicotine. After the initial 2 weeks, nicotine self-administration in male rats declined toward adult-like levels, as the adolescent rats approached adulthood. This study showed that adolescent male rats self-administer significantly more nicotine than do male adult rats, but that adolescent-onset nicotine self-administration in male rats declines over weeks of continued use to approach adult-onset levels. In a previous study, we found that female rats also show greater nicotine self-administration with adolescent onset vs. adult onset, but that the females continued higher rates of self-administration into adulthood. Our results thus reinforce the concept that the adolescent brain is unusually receptive to the effects of nicotine in a manner that reinforces the potential for addiction.

Tuning of RNA editing by ADAR is required in Drosophila

RNA editing increases during development in more than 20 transcripts encoding proteins involved in rapid synaptic neurotransmission in Drosophila central nervous system and muscle. Adar (adenosine deaminase acting on RNA) mutant flies expressing only genome-encoded, unedited isoforms of ion-channel subunits are viable but show severe locomotion defects. The Adar transcript itself is edited in adult wild-type flies to generate an isoform with a serine to glycine substitution close to the ADAR active site. We show that editing restricts ADAR function since the edited isoform of ADAR is less active in vitro and in vivo than the genome-encoded, unedited isoform. Ubiquitous expression in embryos and larvae of an Adar transcript that is resistant to editing is lethal. Expression of this transcript in embryonic muscle is also lethal, with above-normal, adult-like levels of editing at sites in a transcript encoding a muscle voltage-gated calcium channel.

Axonal development in the cerebral white matter of the human fetus and infant

After completion of neuronal migration to form the cerebral cortex, axons undergo rapid elongation to their intra- and subcortical targets, from midgestation through infancy. We define axonal development in the human parietal white matter in this critical period. Immunocytochemistry and Western blot analysis were performed on 46 normative cases from 20-183 postconceptional (PC) weeks. Anti-SMI 312, a pan-marker of neurofilaments, stained axons as early as 23 weeks. Anti-SMI 32, a marker for nonphosphorylated neurofilament high molecular weight (NFH), primarily stained neuronal cell bodies (cortical, subcortical, and Cajal-Retzius). Anti-SMI 31, which stains phosphorylated NFH, was used as a marker of axonal maturity, and showed relatively low levels of staining (approximately one-fourth of adult levels) from 24-34 PC weeks. GAP-43, a marker of axonal growth and elongation, showed high levels of expression in the white matter from 21-64 PC weeks and lower, adult-like levels beyond 17 postnatal months. The onset of myelination, as seen by myelin basic protein expression, was approximately 54 weeks, with progression to "adult-like" staining by 72-92 PC weeks. This study provides major insight into axonal maturation during a critical period of growth, over an age range not previously examined and one coinciding with the peak period of periventricular leukomalacia (PVL), the major disorder underlying cerebral palsy in premature infants. These data suggest that immature axons are susceptible to damage in PVL and that the timing of axonal maturation must be considered toward establishing its pathology relative to the oligodendrocyte/myelin/axonal unit.

Productivity and beyond: mastering the Polish genitive inflection

This study charts the development of the genitive masculine inflection, one of the most irregular parts of the Polish case-marking system. 72 Polish children aged from 2;3 to 10;8 participated in a nonce word production experiment testing their ability to supply the genitive form and their sensitivity to the semantic factors determining the choice of ending. Results indicate that productivity, or the ability to supply the inflected form of some nonce words, emerges early: 78% of the two-year-olds were able to inflect at least one test item. However, mastery, or the ability to consistently supply the correct ending, takes considerably longer to develop, and adultlike levels of provision are not reached until about age 10;0.

Age and Food Deprivation Affects Expression of the Glucocorticosteroid Stress Response in Magellanic Penguin (Spheniscus magellanicus) Chicks

We examined how the glucocortical stress response in free-living Magellanic penguin (Spheniscus magellanicus) chicks changes with age and whether adrenocortical function of chicks within a brood varies in relation to food provisioned by adults. Chicks showed little corticosterone response to capture stress shortly after hatching, an intermediate response around 45-d posthatch, and a robust stress response near fledging. However, in response to an adrenocorticotropic hormone (ACTH) challenge, hatchlings were capable of secreting corticosterone at adult-like levels. The larger sibling in broods of two showed a similar gradual stress-response development pattern. In contrast, by day 45, when differences in body condition were well established between siblings, the smaller, food-deprived chicks significantly increased baseline levels of corticosterone but showed normal stress-induced levels. Near fledging, baseline levels had returned to normal, but stress-induced levels were lower than expected. Similar to altricial species, normally developing semialtricial Magellanic penguin chicks do not express a robust corticosterone stress response until near fledging. Chronic stressors such as food deprivation cause corticosterone use to be up-regulated earlier than expected. However, in cases of extended chronic stress, down-regulation may ensue, thus avoiding the negative effects of chronically elevated levels of corticosterone.

Nativist versus constructivist goals in studying child language

Crain &amp; Thornton (1998: 5) are admirably clear in stating the aims of their research programme: they ‘hope to convince a greater number of students and researchers in child language of the correctness of the Innateness Hypothesis and the theory of Universal Grammar’. As Drozd notes, however, their assumptions under Modularity Matching ‘set the stage for a research programme unlike those typically adopted by developmental psycholinguists’. Whereas C&amp;T are avowedly committed to the continuity assumption (clearly preferring ‘special nativism’ over ‘general nativism’; O'Grady, 1997), constructivists are more interested in the question of how children ‘get from here to there’ (Tomasello, 2003) – that is, from immature levels of language comprehension and use to adultlike levels (and, it is important to note that adultlike levels are not always characterized in generativist terms). Most constructivists are also committed to studying the relations between language development and other simultaneously developing social and cognitive skills (Clark, 2003), whereas nativists tend to be interested in ‘pure’ linguistic ability uncontaminated by nonlinguistic influences. The main goal of nativists then is to verify a specific theory of linguistic competence that suggests that linguistic knowledge is innate and modular and to account for children's linguistic development in terms of UG, whereas the main goal for constructivists is to account for development (change) in the child's language system (beginning from perhaps no predetermined linguistic knowledge) and how it relates to other aspects of development. It is this fundamental difference in goals that makes one quite pessimistic that constructivist and nativist researchers in syntactic development can learn anything from one another; they are simply engaged in separate tasks.

Testosterone Cannot Activate an Adult-Like Stress Response in Prepubertal Male Rats

The pubertal maturation of the hypothalamic-pituitary-adrenal (HPA) axis has received relatively little experimental attention. The present set of experiments sought to extend our understanding of the pubertal stress response by measuring corticotropin (ACTH), corticosterone, and testosterone levels in prepubertal and adult male rats exposed to a single 30-min session of restraint stress. We show that ACTH and corticosterone levels in prepubertal males take significantly longer to return to baseline after termination of the stressor compared to adults. These data indicate that prepubertal males demonstrate a more prolonged stress response compared to adults after a single acute stressor with both psychogenic and neurogenic components. As testosterone has been shown to reduce the stress response in adulthood, we next investigated whether the relatively low levels of circulating testosterone in prepubertal males mediated their protracted stress response. Data collected from additional experiments revealed that prepubertal males treated with adult-like physiological levels of testosterone still exhibited an extended stress response compared to similarly treated adults. These results indicate that the stress response demonstrated by adult males cannot be mimicked or activated in prepubertal males by mere supplementation of testosterone. Thus, we conclude that the HPA neuroendocrine axis is further shaped during pubertal development to allow for the emergence of a more tightly regulated stress response in adulthood.

Postnatal expression of the plasticity-related nerve growth factor-induced gene A (NGFI-A) protein in the superficial layers of the rat superior colliculus: Relation to N-methyl- d-aspartate receptor function

Immediate early gene expression in the CNS is induced by sensory stimulation and seems to be involved in long-term synaptic plasticity. We have used an immunohistochemical method to detect the nerve growth factor-induced gene A (NGFI-A) protein expression in the superficial layers of the rat superior colliculus during postnatal development. Our goal was to correlate the expression of this candidate plasticity protein with developmental events, especially the activity-dependent refinement of the retinocollicular and corticocollicular pathways. We have also investigated the N-methyl- d-aspartate (NMDA)-receptor dependence of the NGFI-A expression. Animals of various postnatal ages were used. Postnatal day (P) 12 and older animals were submitted to a protocol of dark adaptation followed by light stimulation. NGFI-A expression was never observed during the first 2 postnatal weeks. The first stained cells were observed at P15, 2 days after eye opening (P13). The highest number of stained cells was observed at the end of the third postnatal week (P22). Adult-like level of expression was reached at P30, since at this age, the number of stained cells was comparable to that found in adult rats (P90). Both P22 animals submitted to an acute treatment with MK-801 (i.p. injection) and adult animals submitted to chronic intracranial infusion of a MK-801 presented a clear decrease in the NGFI-A expression in response to light stimulation. These results suggest that the NGFI-A expression is dependent on the NMDA receptor activation, and the observed pattern of expression is in close agreement with previous descriptions of the changes in the NMDA receptor-mediated visual activity in the developing rat superior colliculus (SC). Our results suggest that the plasticity-related NGFI-A protein might play a role in the developmental plasticity of the superficial layers of the rat SC after eye opening.

Activity and response to serum of the mammalian thyroid hormone deiodinase 3 gene promoter: identification of a conserved enhancer

Dio3 is an imprinted gene that codes for the type 3 deiodinase (D3), a conserved selenocysteine-containing enzyme that degrades thyroid hormones (TH) into inactive metabolites. D3 is partially responsible for the very low TH levels that are found in utero as it is highly expressed in mammalian uterus, placenta, and fetal tissues. For this reason, it is presumed that D3 protects the developing fetus from high, adult-like levels of TH. To further understand the regulation of D3 expression, we analyzed the promoter activity of 6 kb of 5′-flanking regions of the human and mouse Dio3, by transient transfection studies. Both mouse and human Dio3 promoters are markedly responsive to serum and, to a lesser extent, to phorbol esters and fibroblast growth factor, but only in a cell line in which the endogenous Dio3 mRNA is also responsive to those factors. In addition, we identified a conserved enhancer located 3′ of the gene containing putative AP-1 and serum response elements, and that further increases the serum responsiveness of the Dio3 promoter in a cell-specific manner. The cell-specific serum response of the Dio3 promoter and the identified enhancer may play critical roles in the regulation of gene expression at this imprinted locus.

Adjudicative Competence in the Modern Juvenile Court

In recent years, as juvenile justice systems across the country have become more punitive and courts have held that juveniles are entitled to adult-like levels of due process protection, the adjudicative competence of juveniles has increasingly come into question. To clarify this trend, we reviewed the current state of the law in the fifty states and the District of Columbia, focusing on recent court opinions and legislation as of January of 2000. We then summarize relevant empirical research on juveniles' competency-related capacities in delinquency proceedings. As a case study, we examine the development and implementation of juvenile competence legislation in Virginia, analyzing the legal, clinical, and practical considerations that arise from the recognition of a juvenile competence requirement. We conclude that the passage of a juvenile competence statute does not necessarily lead to an overwhelming number of juveniles being found incompetent. With quality training of evaluators and attorneys, further research on clinical components of adjudicative competency in juveniles, and legislative support and funding, a juvenile competence requirement can help ensure the fair and effective functioning of the modern juvenile court.

Functional development of the auditory brainstem in the tammar wallaby ( Macropus eugenii): the superior olivary complex and its relationship with the auditory brainstem response (ABR)

Twenty pouch-young tammar wallabies ( Macropus eugenii) were used to determine the generator of the auditory brainstem response (ABR) during development through ABR and focal superior olivary complex (SO) recordings. A click response from the SO in the wallaby was recorded from postnatal day (PND) 112 when the ABR was only a positive–negative deflection. Before PND 120, the SO response did not contribute to the ABR as it occurred outside the ABR time-span. After PND 140, the SO response was correlated with multiple waves of the ABR with its dominant component corresponding to the ABR P3 wave. The latency, threshold, and amplitude of the SO response developed to the adult-like level at PND 140, while the rate-following ability in the SO response reached the adult level at PND 160. Presumably this was due to more complicated mechanisms underlying the auditory adaptation. The adaptation of the SO response was directly proportional to the stimulus rate and intensity as well as developmental status. Developmental comparison between the ABR and the focal responses from four auditory brainstem nuclei indicated that each ABR component may have a dominant contributor from the auditory brainstem, but there was no simple and exclusive association between the ABR component and the auditory brainstem nuclei.

Postnatal development of catecholamine inputs to the paraventricular nucleus of the hypothalamus in rats.

Adrenergic and noradrenergic neural projections to the paraventricular nucleus of the hypothalamus (PVN) contribute importantly to viscerosensory modulation of pituitary hormone secretion. Immaturity of ascending catecholamine pathways may partially underlie the documented hyporesponsiveness of PVN neurosecretory cells to certain interoceptive stimuli in rats during the first few weeks of postnatal development. To explore this possibility, the present study compared the distribution and number of dopamine-beta-hydroxylase (DBH)- and phenylethanolamine-N-methyltransferase (PNMT)-positive neurons projecting to the PVN in newborn and adult rats. In addition, a quantitative analysis of DBH- and PNMT-immunoreactive fibers in the medial parvocellular subnucleus, dorsal division (PVNmpd) and posterior magnocellular subnucleus, lateral division (PVNpml) was performed in adult rats and in developing rats on postnatal day (P)1, P7, P14, and P21. The numbers of PVN-projecting neurons in the A1, C1, A2/C2, C3, or A6 catecholamine cell groups were similar in newborn and adult rats, as were the proportions of PVN-projecting neurons in each region that were PNMT-positive. However, fewer PVN-projecting neurons in the C1 and C3 regions expressed DBH immunolabeling in newborn rats compared to adults. DBH immunolabeling increased progressively in the PVNmpd and PVNpml between postnatal days P1 and P21, when adult-like levels were achieved. Conversely, PNMT immunolabeling in the same PVN subdivisions was most dense at P1, gradually decreasing to adult-like levels by P21. These dynamic developmental changes in catecholamine synthetic enzyme immunolabeling densities in the PVN may reflect functional changes in noradrenergic and adrenergic signaling capacity in rats during the first few weeks of postnatal development.

Childrens’ Phoneme Identification in Reverberation and Noise

This study assessed the effects of reverberation, noise, and their combination on listeners' identification of consonants and vowels in naturally produced nonsense syllables presented at different sensation levels (re: speech recognition threshold). A secondary purpose of this study was to assess listeners' identification of voicing, manner, and place of articulation for consonants at 50 dB SL in the reverberation, noise, and combined conditions. Listeners, aged 6-30 years, identified consonant-vowel-consonant-vowel (CVCV) stimuli presented at four different sensation levels (re: speech recognition threshold) of 30, 40, 50, and 60 dB SL in 4 listening conditions: (a) an optimal listening situation (no reverberation, no noise), (b) reverberation only (1.3 seconds), (c) noise only (+13 dB S/N against a multitalker babble), and (d) reverberation plus noise. Results showed that all listener groups achieved maximum consonant identification performance at 50 dB SL. Vowel identification scores were unaffected by SL. Statistical analyses revealed that children's ability to identify consonants varied according to listening condition. For example, children's consonant identification abilities reached adult-like levels of performance at about age 14 years in the reverberation-only and noise-only listening conditions. However, in the reverberation-plus-noise listening condition, children's consonant identification abilities do not mature until the late teenage years. The ability to identify vowels, on the other hand, develops much earlier. A feature analysis of the consonant data showed that for all 3 features (voicing, manner, and place), identification scores were highest in the control condition, similar for the reverberation-only and noise-only conditions, and lowest in the reverberation-plus-noise condition. Voicing was easier for listeners to identify than manner or place of articulation features in reverberation and noise. Taken together, these results suggest that the ability to identify speech in reverberation and noise reaches adult-like level of performance at different ages for different components of the speech signal.

Development of adaptive phonetic gestures in children: evidence from vowel devoicing in two different dialects of Japanese.

High vowels between voiceless consonants are often devoiced in many languages, as well as in many dialects of Japanese. This phenomenon can be hypothesized to be a consequence of the adaptive organization of the laryngeal gestures to various conditions, including dialectal requirements. If this theory is correct, it may be possible to predict developmental changes in vowel devoicing based on the developmental improvement in the dialect-specific organization of the laryngeal gestures. To test this expectation, the developmental properties of vowel devoicing were investigated for 72 children of 4 and 5 years of age, and 37 adults in two dialects of Japanese. One was the Osaka dialect, with a low devoicing rate, and the other the Tokyo dialect, with a high devoicing rate. In the Tokyo dialect, the devoicing rate of children significantly increased and reached an adultlike level by the age of 5 years, whereas it remained low irrespective of age in Osaka. The vowel devoicing of 5-year-old children exhibited the same characteristics as that of the adults of their respective dialect. These results suggest that children growing up with the Tokyo dialect acquire the articulatory gestures which do not inhibit vowel devoicing by the age of 5 years, whereas children growing up with the Osaka dialect acquire those which inhibit the devoicing of vowels by the same age. The results fit in well with the predictions of the gestural account of vowel devoicing. It is also suggested that learning dialect-specific adaptive strategies to coordinate voicing and devoicing gestures as required to attain an adultlike vowel devoicing pattern is a long process: By the age of 5 years children have completed enough of this process to become members of their dialectal community.

Fast corticospinal system and motor performance in children: conduction proceeds skill

Transcranial magnetic stimulation and motor performance tests were used to study the correlation between corticospinal maturation and actual motor performance in a group of young school children (n = 10, mean age = 7 years, age range = 6-9 years). The results were compared with normal adults (n = 10, mean age = 24 years, age range = 22-26 years). In children the central conduction time under the preinnervation condition of facilitation and the postexcitatory silent period was similar to that in adults. However, the central conduction time under relaxation, the latency jump (defined as the difference between the two preinnervation conditions), and the stimulus intensity were statistically different between children and adults ( P < 0.01-0.001). Children did not reach the same level of performance as adults in any of the motor performance tasks (simple acoustic reaction time, tapping, ballistic movement, tracking, and diadochokinesis) ( P < 0.05-0.01). The results indicate that at an early school age, children already possess mature fast corticospinal pathways able to access spinal motoneurons through the pyramidal tract. However, despite the partially adult-like level of neuronal maturation, young school children were not able to perform deliberate motor actions with the same proficiency as adults.

Functional development of the corticocortical pathway for motion analysis in the macaque monkey: a 14C-2-deoxyglucose study.

The corticocortical pathway for motion analysis transmits visual information from striate cortex (V1) via V2, V3d, superior temporal sulcal areas MT, MST, and FST to motion-sensitive areas in the floor and upper bank of the anterior part of the superior temporal sulcus (AST). We studied the functional development of this pathway by applying the 14C-2-deoxyglucose method to rhesus monkeys (Macaca mulatta) ranging in age from 2 d to 3-4 years. A comparison of local cerebral glucose utilization (LCGU) in an intact and a visually deafferented hemisphere in each animal across the age range revealed that this pathway, immature at birth, reaches adult-like levels at 3 months of age. This developmental time course is reflected both in absolute LCGU and in the interhemispheric LCGU differences in all the areas of the pathway. At all ages, the interhemispheric difference in LCGU is largest in V1 and gradually declines along the pathway until a minimum is reached in AST. This decline likely reflects an increasing proportion of nonvisual inputs to the higher-order areas of the pathway. Measurements like those above taken in areas of inferior parietal cortex indicate that they mature at the same rate as those in the motion analysis pathway. However, comparison with findings on the functional development of the temporal areas of the occipitotemporal pathway for object vision (Bachevalier et al., 1991) suggests that areas along the motion analysis pathway and those in parietal cortex mature about 1 month earlier.

Evolution of spontaneous activity in the developing rat superior colliculus.

During the first 10 days after birth in the rat there are a succession of major developmental stages in the retinotectal pathway. During most of this time, the only recordable event in the superior colliculus is spontaneous activity. We studied and characterized this spontaneous activity, hypothesizing that it could play an important role in pathway development. The spontaneous discharges are detectable on postnatal day 5 (P5). After P5, the number of spontaneously active cells per penetration increases up to P10, after which they decrease to adult-like levels by P14-P15. Between P5 and P10, the spontaneous discharges exhibit several patterns of activity, from constant firing to intermittent bursts with periods of quiescence, without any bearing to age. We isolated the retina and superior colliculus by injecting xylocaine onto the optic nerve and found no change in collicular activity. While this suggests that the spontaneous activity in the colliculus is independent of the retina at the ages studied, the opposite experiment, i.e., electrically stimulating the optic nerve, resulted in increased firing by collicular neurons, perhaps via nonclassical synaptic transmission. Finally, we compared interval histograms for spontaneously active cells between P5 and P15. The histograms suggest that at certain ages, spontaneous firing is more regular; moreover, these ages precede major functional advances, e.g., onset of numerous spontaneously firing cells at P6, the first response to optic nerve stimulation at P10, and the first light-evoked response at P12-P13. Our results support the hypothesis that spontaneous activity in the neonatal superior colliculus has a role in development of the retinotectal pathway, but the data also indicate that classical synaptic transmission is not involved.