Inhibitory processes in the flash evoked potential of the monkey.

Flash visual evoked potentials (VEP) and concurrent multiple unit activity (MUA) were recorded from closely spaced intracortical sites in unanesthetized monkeys before and after intracortical injection of the GABAA antagonist bicuculline. Laminar VEP profiles were subjected to current source density (CSD) analysis to localize the transmembrane current flows contributing to the generation of the field potentials. Before bicuculline, the first large VEP component, N40, was generated principally within the parvocellular thalamorecipient sublamina 4Cb. After bicuculline injection, the current sinks associated with N40 spread throughout lamina 4, consistent with a release of intracortical inhibition mediated by GABA. A subsequent component, P65, believed to represent recurrent inhibitory activity within 4Cb, was greatly diminished in size after bicuculline injection. The laminar pattern of current sources and sinks coincident with this component was more complicated after bicuculline, reflecting the summation of current flows associated with disinhibited lamina 4 activity. Bicuculline also altered the responses of neuronal elements in laminae 3 and 5, evidenced by large increases in MUA in these laminae that began approximately 50 msec after stimulation. Finally, bicuculline diminished the degree of intracortical ocular dominance, implicating GABAergic mechanisms in the maintenance and refinement of ocular input segregation within cortical columns.     

Subcortical contributions to the surface-recorded flash-VEP in the awake macaque.

Epidural mapping of flash-VEP in awake monkeys revealed a reliable, short latency negativity, N25 (onset: 18-22 msec; peak: 23-27 msec; duration: 15-20 msec), with a broad frontal surface distribution (frontolateral maximum). N25 was dissociable from the electroretinogram (ERG), from cortical VEP and from the high frequency oscillations (wavelets) coextensive with the ERG and with cortical VEP. Depth recordings traced N25 from its surface maximum down to the lateral geniculate nucleus (LGN). Concomitant VEP, current source density (CSD) and multiunit activity (MUA) profiles obtained with multicontact electrodes showed that the peak and later portion of N25 arise primarily from current sinks (associated with MUA increases) that reflect transmembrane current flow attending depolarization of cells in lamina 6, the uppermost lamina, but may also receive contributions from the more ventral LGN laminae. The initial portion of N25 arises from similar processes near the lamina 3/2 border. Wavelets, in contrast, are prominent in VEP, CSD and MUA within LGN, but attenuate rapidly above LGN. LGN laminar and cellular morphology predict volume conduction of N25 over a wide arc lateral and anterior to LGN and roughly horizontal isopotential planes medial and posterior to LGN. Recordings on the brain surface, within LGN, and in the regions surrounding LGN are consistent with these predictions. Possible contributions from other structures and how these results fit with data obtained in humans are considered.     

Cellular generators of the cortical auditory evoked potential initial component.

Cellular generators of the initial cortical auditory evoked potential (AEP) component were determined by analyzing laminar profiles of click-evoked AEPs, current source density, and multiple unit activity (MUA) in primary auditory cortex of awake monkeys. The initial AEP component is a surface-negative wave, N8, that peaks at 8-9 msec and inverts in polarity below lamina 4. N8 is generated by a lamina 4 current sink and a deeper current source. Simultaneous MUA is present from lower lamina 3 to the subjacent white matter. Findings indicate that thalamocortical afferents are a generator of N8 and support a role for lamina 4 stellate cells. Relationships to the human AEP are discussed.     

Timing and distribution of flash-evoked activity in the lateral geniculate nucleus of the alert monkey

Simultaneous recording of activity from multiple cortical laminae in alert monkeys, using multichannel electrodes, has been used to identify the intracranial generators of surface-recorded, visually evoked potentials (VEP) to stroboscopic flash. Beyond their clinical implications, these results offer an unique view of the timing and sequence of cortical visual processing in the alert monkey, including the somewhat surprising findings of an extremely short-latency response in lamina IVA, a contra- over ipsilateral latency advantage throughout lamina IV, and the lack of a consistent flash-evoked response in the major cortical recipient of the magnocellular system, lamina IVCa. The present study used similar techniques to examine flash-evoked activity in LGN and in optic tract, both to elucidate the role of the subcortical pathways in establishing this pattern, and to provide a parallel, detailed view of the timing of visual activity in LGN and optic tract in the alert monkey. Flash-evoked responses are robust in both parvo- and magnocellular laminae, but these responses differ along several dimensions: (1) parvocellular multiunit activity (MUA) is 1/4 to 1/2 the amplitude of magnocellular MUA; (2) oscillatory activity is higher in frequency and shorter in duration in parvo- than in magnocellular responses; (3) inhibitory processes appear less prominent and diverse in parvo- than in magnocellular activity; (4) mean onset latencies of MUA are longer in parvo- than in magnocellular laminae, but there is extensive overlap in these distributions. Latencies encountered in ipsilateral lamina 3, and at laminar borders dorsal to 3, group more clearly with those of the magnocellular laminae than with those of the other parvocellular laminae. As a result, in the parvocellular division as a whole, the average latency to ipsilateral stimulation is shorter than that to contralateral stimulation. The optic tract exhibits a dorsal-to-ventral progression of onset latency and oscillation frequency consistent with a dorsal/ventral segregation of the inputs to parvo- and magnocellular layers. Comparison of optic tract and LGN data reveals that while many LGN response characteristics are initiated in the retina, significant modification of retinal output occurs at LGN. The techniques used here permit a particularly sensitive and reliable assessment of the timing and distribution of visual responses in the optic tract and LGN of alert monkeys. Our data support the view that in the alert monkey, the surface-VEP to passive, binocular flash primarily reflects activation of parvocellular thalamorecipient laminae of Area 17.(ABSTRACT TRUNCATED AT 400 WORDS)     

Different laminar distribution of flash evoked potentials in cortical areas 17 and 18 b of freely moving rats

The laminar distribution of flash evoked field potential (VEP) was investigated in the visual cortical areas 17 and 18 b in freely moving rats. Averaged VEPs were recorded during stable relaxed wakefulness characterized behaviorally and polygraphically. The depth profiles of the main VEP components displayed polarity reversals in lamina V in every electrode track through area 17 while no polarity reversal was observed in any track through area 18 b. The primary negative component (N30) had an amplitude maximum in lamina IV in both areas. Current source-density analysis (CSD) in connection with amplitude depth profiles indicated that the surface-negative component N30 is generated mainly by the synaptic excitatory inputs in lamina IV. The negative peak of the flash-evoked afterdischarges in area 17 are generated the same way. The data imply a more concentrated field generator in area 17 with densely packed cellular elements responding synchronously to the flash. In area 18 b, either the anatomical distribution or the temporal relationship of the responding elements seems to be different.     

Laminar analysis of the slow wave activity in the somatosensory cortex of anesthetized rats

Rhythmic slow waves characterize brain electrical activity during natural deep sleep and under anesthesia, reflecting the synchronous membrane potential fluctuations of neurons in the thalamocortical network. Strong evidence indicates that the neocortex plays an important role in the generation of slow wave activity (SWA), however, contributions of individual cortical layers to the SWA generation are still unclear. The anatomically correct laminar profiles of SWA were revealed under ketamine/xylazine anesthesia, with combined local field potential recordings, multiple‐unit activity (MUA), current source density (CSD) and time‐frequency analyses precisely co‐registered with histology. The up‐state related negative field potential wave showed the largest amplitude in layer IV, the CSD was largest in layers I and III, whereas MUA was maximal in layer V, suggesting spatially dissociated firing and synaptic/transmembrane processes in the rat somatosensory cortex. Up‐state related firing could start in virtually any layers (III–VI) of the cortex, but were most frequently initiated in layer V. However, in a subset of experiments, layer IV was considerably active in initiating up‐state related MUA even in the absence of somatosensory stimulation. Somatosensory stimulation further strengthened up‐state initiation in layer IV. Our results confirm that cortical layer V firing may have a major contribution to the up‐state generation of ketamine/xylazine‐induced SWA, however, thalamic influence through the thalamorecipient layer IV can also play an initiating role, even in the absence of sensory stimulation.     

The effect of background illumination on pattern onset visual evoked potentials

The early part (first 200 msec) of pattern onset VEPs elicited by a dartboard pattern was studied in conditions of varying level of background illumination. The effect of pattern adaptation and pattern blurr was also studied. The observed complex behaviour of the main negativity within this part of the VEP can be best described in terms of a composite of two independent negative peaks labelled N100 and N130. In high luminance conditions peak N100 was dominant and the presence of N130 was indicated only by a 'notch' on the rising slope of the negativity. As luminance decreased the situation was reversed and N130 became a dominant feature of the negative wave. This finding did not depend on the particular choice of reference site. For checkerboard stimulation the same features were present, but variability of the VEP wave form was greater than in the case of dartboard stimulation. Present results relate the well-known pattern specific properties of the negativity in onset VEPs to N100 only, whereas N130 is not pattern specific. Lower and upper half-field stimulation produced peaks of opposite polarity at 100 msec but no change was observed in polarity of N130. These findings support the suggestion that these two parts of the negativity in pattern onset VEPs may have different cortical sources.     

The topography of visual evoked response properties across the visual field

Visual evoked potentials (VEPs) to luminance and pattern reversal stimulation were derived for a large number of small areas throughout the central visual field. In one study, the field was tested with a stimulus array consisting of 64 equal-area patches. Local response components were extracted by independent m-sequence modulation of the patches. Field topographies were compared between and within subjects using different electrode placements. The subject-dependent local variability observed in response characteristics is attributed to contributions from two or more cortical representations of the visual field and to inter-subject variations in gross cortical anatomy. The second study used luminance modulation of 56 patches across a 15° field, scaled to activate approximately equal cortical areas in area V1. This produced many robust signals at all eccentricities. Bipolar and double differential (“1-dimensional Laplacian”) signals were compared. The double differencing reduced contributions from distant or distributed sources, enhancing nearby current source activity, and greatly improved S/N for many stimulus locations. The high-resolution visual field maps demonstrated that clinical field testing using the VEP is not feasible because of effects of cortical convolutions on responses. However, the vast improvement in data quality and quantity make it a useful tool for VEP source localization and identification.     

Current source density analysis of the hippocampal theta rhythm: associated sustained potentials and candidate synaptic generators

Single-electrode depth profiles of the hippocampal EEG were made in urethane-anesthetized rats and rats trained in an alternating running/drinking task. Current source density (CSD) was computed from the voltage as a function of depth. A problem inherent to AC-coupled profiles was eliminated by incorporating sustained potential components of the EEG. ‘AC’ profiles force phasic current sinks to alternate with current sources at each lamina, changing the magnitude and even the sign of the computed membrane current. It was possible to include DC potentials in the profiles from anesthetized rats by using glass micropipettes for recording. A method of ‘subtracting’ profiles of the non-theta EEG from theta profiles was developed as an approach to including sustained potentials in recordings from freely-moving animals implanted with platinum electrodes. ‘DC’ profiles are superior to ‘AC’ profiles for analysis of EEG activity because ‘DC’-CSD values can be considered correct in sign and more closely represent the actual membrane current magnitudes. Since hippocampal inputs are laminated, CSD analysis leads to straightforward predictions of the afferents involved. Theta-related activity in afferents from entorhinal neurons, hippocampal interneurons and ipsi- and contralateral hippocampal pyramids all appear to contribute to sources and sinks in CA1 and the dentate area. The largest theta-related generator was a sink at the fissure, having both phasic and tonic components. This sink may reflect activity in afferents from the lateral entorhinal cortex. The phase of the dentate mid-molecular sink suggests that medial entorhinal afferents drive the theta-related granule and pyramidal cell firing. The sustained components may be simply due to different average rates of firing during theta rhythm than during non-theta EEG in afferents whose firing rates are also phasically modulated.     

Cortical and subcortical components of the pattern VEP

Studies in the past have shown that wavelength related VEPs can be recorded from both cortical and noncortical sites. Elements of pattern-specific VEPs for both transient and pattern-reversal stimuli are also obtained from these sites. From the noncortical montage consistent responses are obtained with a major component at about 100 msec, which has been found for both the wavelength related and pattern related VEP. In contrast, the cortical VEP to both types of stimuli include two major components, at around 100 and 200 msec. In pattern reversal these components react quite differently to changes in spatial frequency. The component around 100 msec reacts strongly to a wide range of spatial frequencies when recorded from either cortical or noncortical sites. In contrast, the component around 200 msec, obtained with cortical recording, reacts very strongly to high spatial frequencies and very weakly to low spatial frequencies. This finding corresponds to recent results of single-cell studies in the macaque LGN and striate cortex.     

Effect of alcohol and task on hemispheric asymmetry of visually evoked potentials in man.

The study examined the effect of a dose of alcohol producing a mean blood alcohol content of 90 mg% on components of the scalp-recorded visually evoked potential (VEP) both with and without a visual discrimination task to control the level of attention, and the interaction of amplitudinal hemispheric asymmetry of the VEP with alcohol treatment and the discrimination task. Ingestion of ethyl alcohol producing a mean blood alcohol content of 90 mg% affected VEPs recorded from the central scalp by attenuating the overall amplitude of the later VEP components (60-200 msec) and by significantly reducing hemispheric asymmetry in the amplitude of these VEP components. Alcohol attenuates VEP components P90-N120 and N120-P180, and the task of counting flashes and attending to discriminate double flashes increased amplitude of VEP components N60-P90 and P90-N120 in control and placebo conditions. Several studies have reported that the VEP recorded from the right hemisphere of human beings is larger than the VEP recorded from the homologous location in the left hemisphere. Evoked potentials recorded under control and placebo conditions in this study also demonstrated a hemispheric asymmetry with right larger than left for component P90-N120. We also found a reliable alcohol by hemispheric asymmetry interaction. Alcohol selectively depressed the amplitude of the right hemisphere VEP (P90-N120) component to a significantly greater extent than the left hemisphere VEP was affected.     

Cortical sources of the early components of the visual evoked potential

This study aimed to characterize the neural generators of the early components of the visual evoked potential (VEP) to isoluminant checkerboard stimuli. Multichannel scalp recordings, retinotopic mapping and dipole modeling techniques were used to estimate the locations of the cortical sources giving rise to the early C1, P1, and N1 components. Dipole locations were matched to anatomical brain regions visualized in structural magnetic resonance imaging (MRI) and to functional MRI (fMRI) activations elicited by the same stimuli. These converging methods confirmed previous reports that the C1 component (onset latency 55 msec; peak latency 90-92 msec) was generated in the primary visual area (striate cortex; area 17). The early phase of the P1 component (onset latency 72-80 msec; peak latency 98-110 msec) was localized to sources in dorsal extrastriate cortex of the middle occipital gyrus, while the late phase of the P1 component (onset latency 110-120 msec; peak latency 136-146 msec) was localized to ventral extrastriate cortex of the fusiform gyrus. Among the N1 subcomponents, the posterior N150 could be accounted for by the same dipolar source as the early P1, while the anterior N155 was localized to a deep source in the parietal lobe. These findings clarify the anatomical origin of these VEP components, which have been studied extensively in relation to visual-perceptual processes.     

Topography and intracranial sources of somatosensory evoked potentials in the monkey. II. Cortical components

Averaged somatosensory evoked potentials (SEPs) and associated multiple unit activity (MUA) were recorded from a series of epidural and intracortical locations following stimulation of the contralateral median nerve in the monkey. Cortical components were differentiated from the earlier subcortical activity and the intracerebral distribution and sources of each cortical potential were determined. Under barbiturate anesthesia the SEP wave form is simplified and can be wholly attributed to two sources. The earliest cortical activity consists of a biphasic P10-N20 wave which is generated in the posterior bank of the central sulcus. A second wave form, P12-N25, originates in the crown of the postcentral gyrus. No other cortical areas are active. In the alert state the morphology of the surface SEP is complex and reflects the interaction of volume conducted activity from several adjacent cortical sources. The wave form overlying the hand area of the postcentral gyrus consists of P12, P20, P40, N45 and P110. Precentral recordings exhibit P10, P13, N13, N20, P24, N45 and P110. Six anatomical sources have been identified. P10 and N20 originate in the posterior bank of the central sulcus including areas 3a and 3b and are volume conducted in an anteroposterior direction. P12 originates in area 1 as well as the anterior portion of area 2. P20 is generated in the medial portion of the postcentral gyrus including area 5. The source of P40 lies within the lateral portion of the parietal lobe including area 7b. Two components were generated in precentral cortex: P13/N13 originates principally in area 4 within the anterior bank of the central sulcus and P24 reflects activity in the anteromedial portion of the precentral gyrus including area 6. The long latency SEP components, N45 and P110, are generated widely within the somesthetic areas of postcentral cortex. The early cortical SEP components recorded in the monkey closely resemble in configuration and topography those recorded from man although the latter are longer in latency, reflecting interspecies differences in the length of conduction pathways as well as in cortical processing time.     

Principal components analysis of Laplacian waveforms as a generic method for identifying ERP generator patterns: I. Evaluation with auditory oddball tasks.

OBJECTIVE: To evaluate the effectiveness and comparability of PCA-based simplifications of ERP waveforms versus their reference-free Laplacian transformations for separating task- and response-related ERP generator patterns during auditory oddball tasks. METHODS: Nose-referenced ERPs (31 sites total) were recorded from 66 right-handed adults during oddball tasks using syllables or tones. Response mode (left press, right press, silent count) and task was varied within subjects. Spherical spline current source density (CSD) waveforms were computed to sharpen ERP scalp topographies and eliminate volume-conducted contributions. ERP and CSD data were submitted to separate covariance-based, unrestricted temporal PCAs (Varimax) to disentangle temporally and spatially overlapping ERP and CSD components. RESULTS: Corresponding ERP and CSD factors were unambiguously related to known ERP components. For example, the dipolar organization of a central N1 was evident from factorized anterior sinks and posterior sources encompassing the Sylvian fissure. Factors associated with N2 were characterized by asymmetric frontolateral (tonal: frontotemporal R > L) and parietotemporal (phonetic: parietotemporal L > R) sinks for targets. A single ERP factor summarized parietal P3 activity, along with an anterior negativity. In contrast, two CSD factors peaking at 360 and 560 ms distinguished a parietal P3 source with an anterior sink from a centroparietal P3 source with a sharply localized Fz sink. A smaller parietal but larger left temporal P3 source was found for silent count compared to button press. Left or right press produced opposite, region-specific asymmetries originating from central sites, modulating the N2/P3 complex. CONCLUSIONS: CSD transformation is shown to be a valuable preprocessing step for PCA of ERP data, providing a unique, physiologically meaningful solution to the ubiquitous reference problem. By reducing ERP redundancy and producing sharper, simpler topographies, and without losing or distorting any effects of interest, the CSD-PCA solution replicated and extended previous task- and response-related findings. SIGNIFICANCE: Eliminating ambiguities of the recording reference, the combined CSD-PCA approach systematically bridges between montage-dependent scalp potentials and distinct, anatomically-relevant current generators, and shows promise as a comprehensive, generic strategy for ERP analysis.     

Mapped distribution of pattern reversal VEPs to central field and lateral half-field stimuli of different spatial frequencies.

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli of 3 different sizes (1, 2, 4 c/deg) were recorded from 19 scalp derivations in 50 controls. The stimuli were presented on a full-field (FF) screen of 24 degrees visual angle, and on left and right half-fields (HF) of 12 degrees radius. In 15 controls partial HF stimuli were presented on the central 3 and 6 degrees and as hemiannular stimuli of 12 degrees with occlusion of the central 3 and 6 degrees. An antero-posterior polarity reversal of the N1-P1-N2 sequence was observed for FF VEPs. A tangential polarity reversal was observed for HF VEPs. Also with central or hemiannular stimuli polarity reversals of all VEP components were observed within the scalp. Variants of VEP distribution, absence or prominence of some of the ipsi- or contralateral VEP components were observed in 8-40% of controls. The FF and HF VEP distribution, and the variant VEP asymmetries were partly dependent on the pattern spatial frequency.     

Origins of the somatic N20 and high-frequency oscillations evoked by trigeminal stimulation in the piglets.

OBJECTIVE: In humans, the somatic evoked potentials (SEPs) and magnetic fields (SEFs) elicited by peripheral nerve stimulation contain high-frequency oscillations (HFOs) around 600 Hz superimposed on the initial cortical response N20. Responses elicited by snout stimulation in the swine also contain similar HFOs during the rising phase of the porcine N20. This study examined the generators of the N20 and HFOs in the swine. METHODS: We recorded intracortical SEPs and multi-unit activities in the sulcal area of the primary somatosensory cortex (SI) simultaneously with SEFs. The laminar profiles of the potential and current-source-density (CSD) were analyzed. RESULTS: The CSD analysis revealed that the N20 was produced by two dipolar generators, both directed toward the cortical surface. After the arrival of the initial thalamocortical volley in layer IV, the sink of the first generator shifted toward shallower layers II-III with a velocity of 0.109+/-0.038 m/s (mean+/-SD). The sink of the second generator moved to layer V. The initial thalamocortical axonal component of the HFO was produced by repolarizing current with the sink in layer IV. The CSD laminar profile of the postsynaptic component was very similar to the profile of intracortical N20. The current sink within each cycle of HFO propagated upward with a velocity of 0.633+/-0.189 m/s, indicating backpropagation. CONCLUSIONS: We propose that the N20 is generated by two sets of excitatory neurons which also produce the HFOs. Although the loci of synaptic inputs are unknown, these neurons appear to fire initially in the soma and produce backpropagating spikes toward distal apical dendrites. SIGNIFICANCE: These conclusions relate the N20 to the HFO and provide a new explanation of how the current underlying the N20 is invariantly directed toward superficial layers across species.     

Early discrimination of coherent versus incoherent motion by multiunit and synaptic activity in human putative MT+.

A laminar probe was chronically implanted in human putative MT+. The area was specifically responsive to globally coherent visual motion, a crucial aspect of the perception of movement through space. The probe contained 23 microcontacts spaced every 175 microm in a linear array roughly perpendicular to the cortical surface. Current-source density (CSD) and multiunit activity (MUA) were recorded while viewing initially stationary random dot patterns that either moved incoherently or dilated from the central fixation. Onset of visual motion evoked large MUA/CSD activity, with coherent motion evoking earlier and faster-rising MUA/CSD activity than incoherent, in both superficial and deep pyramidal layers. The selective response, peaking at approximately 115 ms, was especially large in deep pyramids, providing evidence that information necessary for visual flow calculations is projected from MT+ at an early latency to distant structures. The early onset of differential MUA/CSD implies that the selectivity of this area does not depend on recurrent inhibition or other intrinsic circuitry to detect coherent motion. The initially greater increase of MUA to coherent stimuli was followed by a greater decrease beginning at approximately 133 ms, apparently because of recurrent inhibition. This resulted in the total MUA being greater to incoherent than coherent stimuli, whereas total rectified CSD was overall greater to coherent than to incoherent stimuli. However, MUA distinguished stationary from moving stimuli more strongly than did CSD. Thus, while estimates of total cell firing (MUA), and of total synaptic activity (CSD) generally correspond to previously reported BOLD results, they may differ in important details.     

The hippocampal CA3 region can generate two distinct types of sharp wave‐ripple complexes,in vitro

Hippocampal sharp wave‐ripples (SPW‐Rs) occur during slow wave sleep and behavioral immobility and are thought to play an important role in memory formation. We investigated the cellular and network properties of SPW‐Rs with simultaneous laminar multielectrode and intracellular recordings in a rat hippocampal slice model, using physiological bathing medium. Spontaneous SPW‐Rs were generated in the dentate gyrus (DG), CA3, and CA1 regions. These events were characterized by a local field potential gradient (LFPg) transient, increased fast oscillatory activity and increased multiple unit activity (MUA). Two types of SPW‐Rs were distinguished in the CA3 region based on their different LFPg and current source density (CSD) pattern. Type 1 (T1) displayed negative LFPg transient in the pyramidal cell layer, and the associated CSD sink was confined to the proximal dendrites. Type 2 (T2) SPW‐Rs were characterized by positive LFPg transient in the cell layer, and showed CSD sinks involving both the apical and basal dendrites. In both types, consistent with the somatic CSD source, only a small subset of CA3 pyramidal cells fired, most pyramidal cells were hyperpolarized, while most interneurons increased firing rate before the LFPg peak. Different neuronal populations, with different proportions of pyramidal cells and distinct subsets of interneurons were activated during T1 and T2 SPW‐Rs. Activation of specific inhibitory cell subsets—with the possible leading role of perisomatic interneurons—seems to be crucial to synchronize distinct ensembles of CA3 pyramidal cells finally resulting in the expression of different SPW‐R activities. This suggests that the hippocampus can generate dynamic changes in its activity stemming from the same excitatory and inhibitory circuits, and so, might provide the cellular and network basis for an input‐specific and activity‐dependent information transmission. © 2014 The Authors Hippocampus Published by Wiley Periodicals, Inc.     

Maturation of visual evoked potentials across adolescence

Adolescence represents the period of transition from childhood to adulthood and is characterized by significant changes in brain structure and function. We studied changes in the functional visual processing in the brain across adolescence. Visual evoked potentials (VEPs) to three types of pattern reversal checkerboard stimuli were measured in 90 adolescents (10-18 years) and 10 adults. Across adolescence, the N75 and P100 VEP peaks decreased in size while the N135 peak increased slightly in size. The latency of VEP peaks showed no reliable change across adolescence. The results suggest that even very basic visual sensory function continues to develop throughout adolescence. The results indicate significant changes in visual parvocellular and magnocellular pathways across adolescence.