Effects of spinal cord stimulation on the cortical somatosensory evoked potentials in failed back surgery syndrome patients

ObjectiveTo evaluate the functional activation of the somatosensory cortical regions in neuropathic pain patients during therapeutic spinal cord stimulation (SCS).MethodsIn nine failed back surgery syndrome patients, the left tibial and the left sural nerves were stimulated in two sessions with intensities at motor and pain thresholds, respectively. The cortical somatosensory evoked potentials were analyzed using source dipole analysis based on 111 EEG signals.ResultsThe short-latency components of the source located in the right primary somatosensory cortex (SI: 43, 54 and 65 ms) after tibial nerve stimulation, the mid-latency SI component (87 ms) after sural nerve stimulation, and the mid-latency components in the right (≈161 ms) and left (≈168 ms) secondary somatosensory cortices (SII) were smaller in the presence of SCS than in absence of SCS. The long-latency source component arising from the mid-cingulate cortex (≈313 ms) was smaller for tibial and larger for sural nerve stimuli during SCS periods compared to periods without SCS.ConclusionsSCS attenuates the somatosensory processing in the SI and SII. In the mid-cingulate cortex, the effect of SCS depends on the type of stimulation and nerve fibers involved.SignificanceResults suggest that the effects of SCS on cortical somatosensory processing may contribute to a reduction of allodynia during SCS.     

Altered neocortical tactile but preserved auditory early change detection responses in Friedreich ataxia

ObjectiveTo study using magnetoencephalography (MEG) the spatio-temporal dynamics of neocortical responses involved in sensory processing and early change detection in Friedreich ataxia (FRDA).MethodsTactile (TERs) and auditory (AERs) evoked responses, and early neocortical change detection responses indexed by the mismatch negativity (MMN) were recorded using tactile and auditory oddballs in sixteen FRDA patients and matched healthy subjects. Correlations between the maximal amplitude of each response, genotype and clinical parameters were investigated.ResultsEvoked responses were detectable in all FRDA patients but one. In patients, TERs were delayed and reduced in amplitude, while AERs were only delayed. Only tactile MMN responses at the contralateral secondary somatosensory cortex were altered in FRDA patients. Maximal amplitudes of TERs, AERs and tactile MMN correlated with genotype, but did not correlate with clinical parameters.ConclusionsIn FRDA, the amplitude of tactile MMN responses at SII cortex are reduced and correlate with the genotype, while auditory MMN responses are not altered.SignificanceSomatosensory pathways and tactile early change detection are selectively impaired in FRDA.     

Maturation of somatosensory cortical processing from birth to adulthood revealed by magnetoencephalography

ObjectiveTo evaluate the maturation of tactile processing by recording somatosensory evoked magnetic fields (SEFs) from healthy human subjects.MethodsSEFs to tactile stimulation of the left index finger were measured from the contralateral somatosensory cortex with magnetoencephalography (MEG) in five age groups: newborns, 6- and 12–18-month-olds, 1.6–6-year-olds, and adults. The waveforms of the measured signals and equivalent current dipoles (ECDs) were analyzed in awake and sleep states in order to separate the effects of age and vigilance state on SEFs.ResultsThere was an orderly, systematic change in the measured and ECD source waveforms of the initial cortical responses with age. The broad U-shaped response in newborns (M60) shifted to a W-shaped response with emergence of a notch by 6 months of age. The adult-type response with M30 and M50 components was present by 2 years. The ECDs of M60 and M30 were oriented anteriorly and that of M50 posteriorly. These maturational changes were independent of vigilance state.ConclusionsThe most significant maturation of short latency cortical responses to tactile stimulation takes place during the first 2 years of life.SignificanceThe maturational changes of somatosensory processing can noninvasively be evaluated with MEG already in infancy.     

Continuous theta-burst rTMS over primary somatosensory cortex modulates tactile perception on the hand

ObjectiveTheta-burst stimulation (TBS) over the primary somatosensory cortex (SI) alters cortical excitability, and in its intermittent form (iTBS) improves tactile spatial acuity. The effects of continuous TBS (cTBS) on tactile acuity remain unknown. The present study examined the influence of cTBS over SI on temporal and spatial tactile acuity on the contralateral hand.MethodsIn separate experiments, temporal discrimination threshold (TDT) and spatial amplitude discrimination threshold (SDT) were obtained from the right hand before and for up to 34 min following real and sham cTBS (600 pulses) over left-hemisphere SI.ResultsCTBS reduced temporal and spatial tactile acuity for up to 18 min following real cTBS. Tactile acuity was unaltered in the groups receiving sham cTBS.ConclusionsCTBS over SI impairs both temporal and spatial domains of tactile acuity for a similar duration.SignificanceCTBS over SI appears to decrease neural activity within targeted cortex and has potential utility in reducing excessive sensory processing.     

Developmental changes in somatosensory processing in cerebral palsy and healthy individuals

ObjectiveCerebral palsy (CP) is a motor disorder that causes physical disability in human development. Recent work has shown that somatosensory deficits are a serious problem for people with CP. There is however no information about the influence of age on brain correlates of tactile sensitivity.MethodsProprioception, touch and pain pressure thresholds, as well as somatosensory evoked potentials (SEP) elicited by tactile stimulation in lips and thumbs were examined in 15 children with CP (range 5–14 y), 14 adults with CP (range 22–55 y), 15 healthy children (range 5–14 y), and 15 healthy adults (range 22–42 y).ResultsChildren with CP as compared to healthy controls showed more reduced sensitivity for non-painful stimuli, but enhanced sensitivity for painful stimuli. Early SEP amplitudes (P50 and P100) were more enhanced in children and adults with CP than in healthy participants. A functional hemispheric asymmetry was observed in CP when left- and right-side body parts were stimulated.ConclusionsData suggest the possibility that altered somatosensory brain processing in CP might be reflecting an enhanced excitability of the somatosensory cortex.SignificanceAssessment of somatosensory functions may have implications for future neuromodulatory treatment of pain complaints and motor rehabilitation programs in children and adults with cerebral palsy.     

Somatotopic representation of pain in the primary somatosensory cortex (S1) in humans

ObjectiveIn contrast to tactile inputs, the organization and processing of nociceptive inputs in the primary somatosensory cortex (S1) remain largely unexplored. Few studies have examined the arrangement of nociceptive inputs in S1. The aim of this study was to investigate the representation of nociceptive inputs in the human cortex, including the somatosensory and posterior parietal cortices, from widely separated cutaneous sites.MethodsWe examined the somatotopic organization of the nociceptive system in S1, opercular and posterior parietal cortices by measuring the magnetoencephalographic responses (somatosensory-evoked magnetic fields) of four healthy controls in response to intraepidermal electrical stimulation applied to the face, neck, back, elbow, wrist, hand, finger, knee, and foot, which selectively activated the Aδ fibers.ResultsMagnetoencephalography demonstrated clear somatotopy in the S1 responses to noxious stimuli, with the foot representation in the extreme posteromedial position of S1 and the facial area in the extreme anterolateral position. There was little evidence of any clear somatotopic organization in the secondary somatosensory and posterior parietal cortices.ConclusionThese findings suggest that the nociceptive system uses the large body surface map in S1.SignificanceThis is the first MEG study to demonstrate the cortical representation of nociceptive inputs in the human S1. We showed that widely separated cutaneous sites clearly supported Penfield’s homunculus.     

Evaluation of lip sensory disturbance using somatosensory evoked magnetic fields

ObjectiveTo evaluate lip sensory dysfunction in patients with inferior alveolar nerve injury by lip-stimulated somatosensory evoked fields (SEFs).MethodsSEFs were recorded following electrical lip stimulation in 6 patients with unilateral lip sensory disturbance and 10 healthy volunteers. Lip stimulation was applied non-invasively to each side of the lip with the same intensity using pin electrodes.ResultsAll healthy volunteers showed the earliest response clearly and consistently at around 25 ms (P25m) and at least one of the following components, P45m, P60m, or P80m, over the contralateral hemisphere. The ranges of the peak latencies were 23–33, 42–50, 56–67, and 72–98 ms for right-side stimulation and 23–34, 46–49, 52–68, and 71–90 ms for left-side stimulation. Affected-side stimulation did not evoke P25m component in any patients, but invoked traceable responses in 5 patients whose latencies were 57, 89, 65, 53, and 54 ms. Unaffected-side stimulation induced P25m in 2 patients at 27 and 25 ms, but not in the other 4 patients.ConclusionThe P25m component of lip SEFs can be an effective parameter to indicate lip sensory abnormality.SignificanceLip sensory dysfunction can be objectively evaluated using magnetoencephalography.     

Low and high-frequency somatosensory evoked potentials recorded from the human pedunculopontine nucleus

ObjectiveTo investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg).MethodsTwenty-two patients, suffering from Parkinson’s disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation.ResultsSEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05 ± 0.61 ms) shifted of 0.18 ± 0.07 ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4 ± 0.2 ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials.ConclusionWhile the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level.SignificanceOur results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area.     

Secondary somatosensory cortex evoked responses and 6-year neurodevelopmental outcome in extremely preterm children

ObjectiveWe assessed in extremely preterm born (EPB) children whether secondary somatosensory cortex (SII) responses recorded with magnetoencephalography (MEG) at term-equivalent age (TEA) correlate with neurodevelopmental outcome at age 6 years. Secondly, we assessed whether SII responses differ between 6-year-old EPB and term-born (TB) children.Methods39 EPB children underwent MEG with tactile stimulation at TEA. At age 6 years, 32 EPB and 26 TB children underwent MEG including a sensorimotor task requiring attention and motor inhibition. SII responses to tactile stimulation were modeled with equivalent current dipoles. Neurological outcome, motor competence, and general cognitive ability were prospectively evaluated at age 6 years.ResultsUnilaterally absent SII response at TEA was associated with abnormal motor competence in 6-year-old EPB children (p = 0.03). At age 6 years, SII responses were bilaterally detectable in most EPB (88%) and TB (92%) children (group comparison, p = 0.69). Motor inhibition was associated with decreased SII peak latencies in TB children, but EPB children lacked this effect (p = 0.02).ConclusionsUnilateral absence of an SII response at TEA predicted poorer motor outcome in EPB children.SignificanceNeurophysiological methods may provide new means for outcome prognostication in EPB children.     

Neurophysiologic markers in laryngeal muscles indicate functional anatomy of laryngeal primary motor cortex and premotor cortex in the caudal opercular part of inferior frontal gyrus

ObjectiveThe aim of this study was to identify neurophysiologic markers generated by primary motor and premotor cortex for laryngeal muscles, recorded from laryngeal muscle.MethodsTen right-handed healthy subjects underwent navigated transcranial magnetic stimulation (nTMS) and 18 patients underwent direct cortical stimulation (DCS) over the left hemisphere, while recording neurophysiologic markers, short latency response (SLR) and long latency response (LLR) from cricothyroid muscle. Both healthy subjects and patients were engaged in the visual object-naming task. In healthy subjects, the stimulation was time-locked at 10–300 ms after picture presentation while in the patients it was at zero time.ResultsThe latency of SLR in healthy subjects was 12.66 ± 1.09 ms and in patients 12.67 ± 1.23 ms. The latency of LLR in healthy subjects was 58.5 ± 5.9 ms, while in patients 54.25 ± 3.69 ms. SLR elicited by the stimulation of M1 for laryngeal muscles corresponded to induced dysarthria, while LLR elicited by stimulation of the premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, corresponded to speech arrest in patients and speech arrest and/or language disturbances in healthy subjects.ConclusionIn both groups, SLR indicated location of M1 for laryngeal muscles, and LLR location of premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, while stimulation of these areas in the dominant hemisphere induced transient speech disruptions.SignificanceDescribed methodology can be used in preoperative mapping, and it is expected to facilitate surgical planning and intraoperative mapping, preserving these areas from injuries.     

Cortical rhythm of No-go processing in humans: An MEG study

ObjectiveWe investigated the characteristics of cortical rhythmic activity in No-go processing during somatosensory Go/No-go paradigms, by using magnetoencephalography (MEG).MethodsTwelve normal subjects performed a warning stimulus (S1) – imperative stimulus (S2) task with Go/No-go paradigms. The recordings were conducted in three conditions. In Condition 1, the Go stimulus was delivered to the second digit, and the No-go stimulus to the fifth digit. The participants responded by pushing a button with their right thumb for the Go stimulus. In Condition 2, the Go and No-go stimuli were reversed. Condition 3 was the resting control.ResultsA rebound in amplitude was recorded in the No-go trials for theta, alpha, and beta activity, peaking at 600–900 ms. A suppression of amplitude was recorded in Go and No-go trials for alpha activity, peaking at 300–600 ms, and in Go and No-go trials for beta activity, peaking at 200–300 ms.ConclusionThe cortical rhythmic activity clearly has several dissociated components relating to different motor functions, including response inhibition, execution, and decision-making.SignificanceThe present study revealed the characteristics of cortical rhythmic activity in No-go processing.     

A comparison of relative-frequency and threshold-hunting methods to determine stimulus intensity in transcranial magnetic stimulation

ObjectiveStimulation intensity (SI) in transcranial magnetic stimulation is commonly set in relation to motor threshold (MT), or to achieve a motor-evoked potential (MEP) of predefined amplitude (usually 1 mV). Recently, IFCN recommended adaptive threshold-hunting over the previously endorsed relative-frequency method. We compared the Rossini–Rothwell (R–R) relative-frequency method to an adaptive threshold-hunting method based on parameter estimation by sequential testing (PEST) for determining MT and the SI to target a MEP amplitude of 1 mV (I_1 mV).MethodsIn 10 healthy controls we determined MT and I_1 mV with R–R and PEST using a blinded crossover design, and performed within-session serial PEST measurements of MT.ResultsThere was no significant difference between methods for MT (52.6 ± 2.6% vs. 53.7 ± 3.1%; p = 0.302; % maximum stimulator output; R–R vs. PEST, respectively) or I_1 mV (66.7 ± 3.0% vs. 68.8 ± 3.8%; p = 0.146). There was strong correlation between R–R and PEST estimates for both MT and I_1 mV. R–R required significantly more stimuli than PEST. Serial measurements of MT with PEST were reproducible.ConclusionsPEST has the advantage of speed without sacrificing precision when compared to the R–R method, and is adaptable to other SI targets.SignificanceOur results in healthy controls add to increasing evidence in favour of adaptive threshold-hunting methods for determining SI.     

Multiple frequency functional connectivity in the hand somatosensory network: An EEG study

ObjectiveTo investigate the dynamics of communication within the primary somatosensory neuronal network.MethodsMultichannel EEG responses evoked by median nerve stimulation were recorded from six healthy participants. We investigated the directional connectivity of the evoked responses by assessing the Partial Directed Coherence (PDC) among five neuronal nodes (brainstem, thalamus and three in the primary sensorimotor cortex), which had been identified by using the Functional Source Separation (FSS) algorithm. We analyzed directional connectivity separately in the low (1–200 Hz, LF) and high (450–750 Hz, HF) frequency ranges.ResultsLF forward connectivity showed peaks at 16, 20, 30 and 50 ms post-stimulus. An estimate of the strength of connectivity was modulated by feedback involving cortical and subcortical nodes. In HF, forward connectivity showed peaks at 20, 30 and 50 ms, with no apparent feedback-related strength changes.ConclusionsIn this first non-invasive study in humans, we documented directional connectivity across subcortical and cortical somatosensory pathway, discriminating transmission properties within LF and HF ranges.SignificanceThe combined use of FSS and PDC in a simple protocol such as median nerve stimulation sheds light on how high and low frequency components of the somatosensory evoked response are functionally interrelated in sustaining somatosensory perception in healthy individuals. Thus, these components may potentially be explored as biomarkers of pathological conditions.     

Methodology for intraoperatively eliciting motor evoked potentials in the vocal muscles by electrical stimulation of the corticobulbar tract

ObjectiveTo establish a methodology for recording corticobulbar motor evoked potentials (CoMEPs) from vocal muscles after transcranial electrical stimulation (TES) and direct cortical stimulation (DCS).MethodsTwenty-four patients were included in this study (22 for TES, 2 for DCS, 3 for TES plus DCS) that underwent different surgical procedures. We used two methods to elicit CoMEPs: (a) TES by stimulation over C3/Cz or C4/Cz and (b) DCS with a strip electrode placed over the primary motor area (M1) for laryngeal muscles. To record CoMEPs from vocal muscles we used two hook wire electrodes 76 μm of diameter passing through 27 gauge needle endotracheally placed in the vocal muscles after intubation.ResultsRecording of CoMEPs in the vocal muscles after TES was successfully performed in 22 patients. TES over the right or left hemisphere elicit responses bilaterally. The onset latencies for the right vocal muscle was 12.4 ± 3.1 ms (ipsilateral stimulation) and 12.7 ±2.2 ms (contralateral stimulation) while for the left vocal muscle, onset latency was 12.9 ± 2.3 ms (ipsilateral stimulation) and 14.1 ± 3.4 ms (contralateral stimulation). In five patients DCS elicited CoMEPs in right and left vocal muscle with latency of 16.6 ± 4.7 and 15.6 ± 3.7 ms, respectively.ConclusionThe method to elicit and record CoMEPs in vocal muscles shows reliable results and adds one more tool in the armamentarium of intraoperative neurophysiology.SignificanceThis method shows the ability to continuously monitor the functional integrity of corticobulbar pathways, vagal nucleus and laryngeal nerves.     

Magnetic source imaging of tactile input shows task-independent attention effects in SII

We investigated whether attention to different stimulus attributes (location, intensity) has different effects on the activity of the secondary (SII) somatosensory cortex. Tactile stimuli were applied to the left index finger and somatosensory evoked fields (SEFs) were recorded using a whole-head magnetoencephalography (MEG) system. Two oddball paradigms with stimuli varying in location or intensity were performed in an ignore and an attend condition. Brain sources were estimated by magnetic source imaging. No attention effect was observed for the primary SI area. However, attention enhanced SII activity bilaterally from 55 to 130 ms by 52% in the spatial and 64% in the intensity discrimination task. SII attentional enhancement was very similar in both paradigms and occurred both for deviants and standards.     

Functional characterization of human second somatosensory cortex by magnetoencephalography

Magnetoencephalographic (MEG) recordings allow noninvasive monitoring of simultaneously active brain areas with reasonable spatial and excellent temporal resolution. Whole-scalp neuromagnetic recordings show activation of contralateral primary (SI) and bilateral second (SII) somatosensory cortices to unilateral median nerve stimulation. Recent MEG studies on healthy and diseased human subjects have shown some functional characteristics of SII cortex. Besides tactile input, the SII cortex also responds to nociceptive afferents. The SII activation is differentially modulated by isometric muscle contraction of various body parts. Lesions in the SII cortex may disturb the self-perception of body scheme. Moreover, the SI and SII cortices may be sequentially activated within one hemisphere, but the SII cortex may also receive direct peripheral input on the ipsilateral side.     

Parallel spinal pathways generate the middle-latency N1 and the late P2 components of the laser evoked potentials

ObjectiveTo investigate the possible presence of multiple spino-thalamic pathways with different conduction velocities (CVs) in the human spinal cord.MethodsLaser evoked potentials (LEPs) were recorded in 10 healthy subjects after stimulation of the dorsal midline at four vertebral level: C5, T2, T6, and T10. This method allowed us to minimize the influence of the conduction in the peripheral fibers and to calculate the spinal CV in two different ways: (1) the reciprocal of the slope of the regression line was obtained from the latencies of the different LEP components, and (2) the distance between C5 and T10 was divided by the latency difference of the responses at the two sites. In particular, we considered the middle-latency N1 potential (latencies of around 135, 150, 157, and 171 ms after stimulation at C5, T2, T6, and T10 levels, respectively), which is generated in the second somatosensory (SII) area, and the late P2 response (latencies of around 336, 344, 346, and 362 ms after stimulation at C5, T2, T6, and T10 levels, respectively), which is generated in the anterior cingulate cortex (ACC).ResultsThe calculated CV of the spinal fibers generating the N1 potential (around 9 m/s) was significantly different (P < 0.05) from the one of the pathway producing the P2 response (around 13 m/s).ConclusionsOur results suggest that the N1 and the P2 LEP components are generated by two parallel spinal pathways.SignificanceBoth the N1 and P2 potentials should be recorded in the clinical routine since a dissociated abnormality of either response may be found in lesions of the nociceptive system not only in the brain, but also at spinal cord level.     

In vivo human hippocampal cingulate connectivity: A corticocortical evoked potentials (CCEPs) study

ObjectiveTo investigate the human limbic system using cortico-cortical evoked potential (CCEP), which reveals the brain networks.MethodsFive patients with nonlesional medically intractable focal epilepsy with ictal onset outside the limbic system were enrolled. All patients underwent stereoelectroencephalogram electrode implantation in order to delineate the epileptogenic zone. Alternating 1 Hz electrical stimuli were delivered to the hippocampus and posterior cingulate gyrus. A total of sixty stimuli were averaged in each trial to obtain CCEP responses.ResultsHippocampal stimulation elicited prominent CCEP responses in the posterior cingulate gyrus. The latencies of early (N1) and late (N2) negative peak ranged 20–60 ms and 102–175 ms respectively. In addition, CCEP responses were observed in the posterior parahippocampal gyrus, medial superior frontal gyrus (SFG) and orbitofrontal cortex. Stimulation of posterior cingulate contacts induced CCEPs in the hippocampus with N1 and N2 latencies of 25–43 ms and 90–234 ms respectively in all five patients.ConclusionThis finding supports the assertion that the hippocampus is connected with the posterior cingulate gyrus, posterior parahippocampal gyrus, medial SFG and orbitofrontal cortex. The hippocampus and posterior cingulate gyrus have a bidirectional network through the cingulum.SignificanceThe present study provides new insight into the human limbic network.     

Differentiated effects of deep brain stimulation and medication on somatosensory processing in Parkinson’s disease

ObjectivesDeep brain stimulation (DBS) and dopaminergic medication effectively alleviate the motor symptoms in Parkinson’s disease (PD) patients, but their effects on the sensory symptoms of PD are still not well understood. To explore early somatosensory processing in PD, we recorded magnetoencephalography (MEG) from thirteen DBS-treated PD patients and ten healthy controls during median nerve stimulation.MethodsPD patients were measured during DBS-treated, untreated and dopaminergic-medicated states. We focused on early cortical somatosensory processing as indexed by N20m, induced gamma augmentation (31–45 Hz and 55–100 Hz) and induced beta suppression (13–30 Hz). PD patients’ motor symptoms were assessed by UPDRS-III.ResultsUsing Bayesian statistics, we found positive evidence for differentiated effects of treatments on the induced gamma augmentation (31–45 Hz) with highest gamma in the dopaminergic-medicated state and lowest in the DBS-treated and untreated states. In contrast, UPDRS-III scores showed beneficial effects of both DBS and dopaminergic medication on the patients’ motor symptoms. Furthermore, treatments did not affect the amplitude of N20m.ConclusionsOur results suggest differentiated effects of DBS and dopaminergic medication on cortical somatosensory processing in PD patients despite consistent ameliorating effects of both treatments on PD motor symptoms.SignificanceThe differentiated effect suggests differences in the effect mechanisms of the two treatments.     

Neuromagnetic biomarkers of visuocortical development in healthy children

ObjectiveThe objective of the present study was to investigate noninvasive biomarkers for visuocortical development in healthy children.MethodsSixty healthy children and 20 adults were studied with a whole-head magnetoencephalography (MEG) system. The adults were included to find out when the markers stabilize. Visual evoked magnetic fields (VEFs) were evoked with full-field pattern-reversal checks.ResultsThree response peaks were identified at 77 ± 8 ms (M75), 111 ± 9 ms (M100) and 150 ± 11 ms (M145) for children. The latency of M75 and M100 decreased with age (p < 0.01). The amplitude ratio of M100/M75 increased significantly with age (p < 0.001). The differences of MEG source images between the left and right occipital cortices for M75 and M145 increased significantly with age (r = 0.47 and 0.46, respectively, p < 0.01).ConclusionsThe latency of M75 and M100 and the amplitude ratio of M100/M75 are robust biomarkers for the development of visual function in children.SignificanceThe development of visual function in childhood is noninvasively measurable. The results lay a foundation for quantitative identification of developmental delay and/or abnormalities of visual function in children with brain disorders.