April 18, 2026
infrared spectroscopy (fNIRS) recording with Part multichannel opt-ode cap (AI up-scaled from [133]). (D) An infant is prepared for functional magnetic resonance imaging (fMRI) (AI up-scaled from [137]). Abbreviation: AI, artificial intelligence. Figure 1. The case for early emergence. The most compelling evidence for early emergence comes from studies of: (i) functional connectivity networks in fetuses
[143] and newborns [40,41]; (ii) attention in young infants [53,144]; (iii) multi-sensory integration in young infants (namely, the McGurk effect) [59,60]; and (iv) global neural prediction errors in fetuses [65], newborns [64], and young infants [63]. The P300 scalp topography shown to the left of the bottom row is adapted from
[145] (CC BY 4.0), and the cartoon images of developing brains are adapted from [3] (CC BY-NC 4.0). All other images are generative artificial intelligence (Mid-journey). Abbreviations: GA, gestational age; PMA, post-menstrual age.
Of course, even if the networks required for consciousness are in place from birth (or soon after) [41–43], it might be argued that they do not play a significant role in cognitive processing. How- ever, a study of infants in a neonatal intensive care unit with suspected neurological injury found that disruption to the ECN at term-equivalent age was predictive of the emergence of motor impairments at 4 and 8 months of age [44], suggesting a causal link between the ECN and behavior even at this young age.
A second line of evidence for the early emergence of consciousness involves attention. Although the mechanisms of consciousness are widely taken to be distinct from those of attention [45,46],
there are close links between the two phenomena, and it is plausible to suppose that the emergence of consciousness broadly tracks that of attention. This is particularly the case with respect to top-down (endogenous, voluntary) attention, which emerges at about 3–6 months of age [47,48]. If bottom-up (exogenous, involuntary) attention is also sufficient for consciousness, as has sometimes been suggested [49,50], then we have grounds for locating the emergence of consciousness significantly earlier, for bottom-up attention is evident from eye movements in newborns [51]. However, caution must be exercised here, as sub-cortical (and thus, presumably, unconscious) pathways may be driving the earliest forms of bottom-up attention [52]. That said, a recent study [53] found that stimulus-driven attention in infants recruits the same fronto-parietal and cingulo-opercular networks that are recruited in adults, thus suggesting that a link between bottom-up attention and consciousness might be in place as early as 3 months.
A third line of evidence for early-onset accounts of consciousness comes from research on multi-sensory integration. Certain forms of multi-sensory integration, such as the detection of temporal synchrony between auditory and visual streams, can occur outside of consciousness [54–56] and their presence in early infancy provides little evidence for infant consciousness. However, other forms of multi-sensory integration do appear to occur only when the integrated stimuli are consciously perceived [57]. For example, the McGurk effect disappears when flash suppression is used to prevent the visual stimulus from reaching awareness [58]. This is directly relevant to the question of infant consciousness, for consistent McGurk-type effects can be found at 5 months of age [59,60] and even sometimes from 4 months, albeit intermittently [61].
A fourth line of evidence for the early emergence of consciousness exploits an auditory odd- ball paradigm (the ‘local-global’ paradigm). First developed in connection with disorders of consciousness [62], the local-global paradigm exploits a P300 (or ‘P3b’) response, a late cortical response often associated with surprise and the reorientation of attention. Although P300 responses to first-order (‘local’ or within-trial) auditory oddballs do not appear to be predictive of consciousness (e.g., they can be found in UWS patients), P300 responses to second-order (‘global’ or between-trial) auditory oddballs (the ‘global effect’) exhibit greater specificity to consciousness [e.g., these responses can be found in minimally conscious state (MCS) patients but not UWS patients] [62]. For this reason, the global effect is widely taken to be suggestive of perceptual consciousness. Strikingly, an early ERP event-related potential (ERP) study found evidence of a P300-like ‘negative slow wave’ responses to global oddballs in 3-month-old infants [63], while more recent studies using magneto-encephalography (MEG) have found evidence of a P300-like response to global oddballs in newborns [64] and fetuses past 35 weeks gestational age [65].
Even when we consider the strongest evidence from local-global paradigms, however, the corresponding findings [63–65] must be qualified in two ways. Firstly, the parameters (mainly, the latency) of the infant response differ from those of the adult P300 response, as axonal conduction velocities are slower in the immature brain [66], resulting in delayed cortical components as compared with adults. And yet, despite different latencies, a plausible case can be made for thinking that the infant’s P300-like response plays the same functional role as the adult’s P300 response. Second, the specificity of the global effect as an indicator of consciousness has been questioned, for there is some evidence that the global effect can be obtained in the absence of consciousness [67]. These findings are important, but they do not undermine our case for the early emergence of consciousness, because our claim is only that late cortical responses to global oddballs are widely regarded as having better than chance accuracy for detecting consciousness, and, as such, should inform our ‘best guess’ regarding the presence of consciousness in the developing human.
Because P300-like responses to global oddballs indicate that higher-order networks are online and are able to communicate with auditory networks, evidence of the global effect in early infancy converges with other findings in infants (reviewed above) indicating that attentional and higher- order regions mature earlier than had been thought. These findings are also of a piece with pre- dictive processing approaches to perceptual consciousness [68].
It is important to recognize that at least some (and perhaps all) of these markers are experience- dependent and their emergence can be delayed/altered by a variety of factors. For example, pre- mature birth has been associated with disruption to the DMN and frontoparietal networks [40,69] and with an absence of the neural response to surprising sensory omissions that is usu- ally seen at 6 months [70]. The fact that some of the markers of consciousness can be delayed/ altered by adverse environmental conditions does not imply that consciousness itself is de- layed (recall that we are treating these markers as one-way rather than two-way markers), but we should certainly take seriously the possibility that consciousness emerges at different times in different individuals. Care must be taken in making comparisons between infants based on age alone
Finally, we note the possibility of applying a perturbational approach to the question of infant con- sciousness. The most sophisticated perturbational approach to the detection of consciousness thus far is the perturbational complexity index (PCI), in which the cortex is perturbed by the application of transcranial magnetic stimulation (TMS) pulses and the complexity of the cortical response is then measured by electroencephalography (EEG) [71]. Data from studies involving the loss and recovery of consciousness in the context of general anesthesia, non-rapid eye move- ment sleep, and disorders of consciousness suggest that an individual’s PCI response can inform ascriptions of consciousness [71–74]. Because the risk profile of TMS in early development is unknown, its use in infants and fetuses is regarded as unethical when not medically justified. However, a sensory version of the PCI approach might be viable, in which the infant (or fetal) cortex would be perturbed not by TMS, but by the presentation of a visual, auditory, or even olfactory stimulus [75]. Although this ‘sensory PCI’ approach has yet to be rigorously imple- mented, it may prove to be an important tool in the quest to detect the earliest forms of consciousness [76].
What is it like to be a baby?
Thus far we have focused on the ‘when’ of infant consciousness, but the ‘what’ of infant consciousness raises equally important – and, in certain ways, more tractable – issues. Here, we bracket questions about whether infants of a certain age are conscious and focus instead on the question of what the character of their experience is like (assuming that they are conscious).
The content of infant experience is, of course, constrained by the immature state of various per- ceptual systems. In vision, acuity is low at birth. Color detection is also limited at birth and mature trichromatic processing does not emerge until about 3 months of age [77,78]. However, category-specific responses to faces, scenes, and bodies have been seen using fMRI in the ven- tral visual pathway from as early as 2 months [79] (see also [80]). Intriguingly, differences in the long-range neural connectivity of different category-specific regions are present about 1 week after birth, suggesting that some of the broader associations may already be evoked [81].
Given that the auditory system matures before the visual system, there is reason to suspect that the infant’s auditory experience might be richer and more complex than their visual
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