Biology subjects

Shareef, I.

Publications and source records attributed to Shareef, I..

4 recordsLinked to original sources

bioRxiv2024

Altered visual cortex excitatory/inhibitory ratio following transient congenital visual deprivation in humans

Non-human animal models have indicated that the ratio of excitation to inhibition (E/I) in neural circuits is experience dependent and changes across development. Here, we assessed 3T Magnetic Resonance Spectroscopy (MRS) and electroencephalography (EEG) markers of cortical E/I ratio in ten individuals who had been treated for dense bilateral congenital cataracts, after an average of 12 years of blindness, to test for dependence of the E/I ratio in humans on early visual experience. First, participants underwent MRS scanning at rest with their eyes opened and eyes closed, to obtain visual cortex Gamma-Aminobutyric Acid (GABA+) concentration, Glutamate/Glutamine (Glx) concentration and the concentration ratio of Glx/GABA+, as measures of inhibition, excitation, and E/I ratio respectively. Subsequently, EEG was recorded to assess aperiodic activity (1-20 Hz) as a neurophysiological measure of the cortical E/I ratio, during rest with eyes open and eyes closed, and during flickering stimulation. Across conditions, congenital cataract-reversal individuals demonstrated a significantly lower visual cortex Glx/GABA+ ratio, and a higher intercept and steeper aperiodic slope at occipital electrodes, compared to age-matched sighted controls. In the congenital cataract-reversal group, a lower Glx/GABA+ ratio was associated with better visual acuity, and Glx concentration correlated positively with the aperiodic intercept in the conditions with visual input. We speculate that these findings result from an increased E/I ratio of the visual cortex as a consequence of congenital blindness, which might require commensurately increased inhibition in order to balance the additional excitation from restored visual input. The lower E/I ratio in congenital cataract-reversal individuals would thus be a consequence of homeostatic plasticity.

neuroscience↗

bioRxiv2023

Stimulus-evoked and resting-state alpha oscillations show a linked dependence on patterned visual experience for development

Persistent visual impairments after congenital blindness due to dense bilateral cataracts have been attributed to altered visual cortex development within a sensitive period. Occipital alpha (8-14 Hz) oscillations were found to be reduced after congenital cataract reversal during visual motion tasks. However, it has been unclear whether reduced alpha oscillations were task-specific, or linked to impaired visual behavior in cataract-reversed individuals. Here, we compared resting-state and stimulus-evoked alpha activity between individuals who had been treated for dense bilateral congenital cataracts (CC, n = 13, mean duration of blindness = 11.0 years) and age-matched, normally sighted individuals (SC, n = 13). We employed the visual impulse response function, adapted from VanRullen and MacDonald (2012), to test for the characteristic alpha response to visual white noise. Participants observed white noise stimuli changing in luminance with equal power at frequencies between 0-30 Hz. Compared to SC individuals, CC individuals demonstrated a reduced likelihood of exhibiting an evoked alpha response. Moreover, stimulus-evoked alpha power was reduced and correlated with a corresponding reduction of resting-state alpha power in the same CC individuals. Finally, CC individuals with an above-threshold evoked alpha peak had better visual acuity than CC individual without an evoked alpha peak. Since alpha oscillations have been linked to feedback communication, we suggest that the concurrent impairment in resting-state and stimulus-evoked alpha oscillations indicates an altered interaction of top-down and bottom-up processing in the visual hierarchy, which likely contributes to incomplete behavioral recovery in individuals who had experienced transient congenital blindness.

neuroscience↗

bioRxiv2021

The Size-Weight Illusion is unimpaired in individuals with a history of congenital visual deprivation

Visual deprivation in childhood can lead to lifelong impairments in visual and multisensory processing. Here, the Size-Weight-Illusion was used to test whether visuo-haptic integration recovers after sight restoration. In Experiment 1, congenital (CC: 7 (3F), 8-35 years) and developmental cataract reversal individuals (DC: 9 (2F), 8-37 years), as well as congenitally blind (CB: 2 (1F), 33 and 44 years) and normally sighted individuals (SC: 10 (7F), 19-36 years) perceived larger objects as lighter than smaller objects of the same weight. In Experiment 2, CC (6 (1F), 17-44.7 years) and SC (7 (5F), 21-29 years) individuals performed identically when tested without haptic size cues. Together, this suggested that early visual experience is not necessary to perceive the Size-Weight-Illusion.

neuroscience↗

bioRxiv2019

Cross-modal temporal biases emerge during early sensitive periods

Human perception features stable biases, such as perceiving visual events as later than synchronous auditory events. The origin of such perceptual biases is unknown, they could be innate or shaped by sensory experience during a sensitive period. To investigate the role of sensory experience, we tested whether a congenital, transient loss of vision, caused by bilateral dense cataracts, has sustained effects on the ability to order events spatio-temporally within and across sensory modalities. Most strikingly, individuals with reversed congenital cataracts showed a bias towards perceiving visual stimuli as occurring earlier than auditory (Exp. 1) and tactile (Exp. 2) stimuli. In contrast, both normally sighted controls and individuals who could see at birth but developed cataracts during childhood reported the typical bias of perceiving vision as delayed compared to audition. Thus, we provide strong evidence that cross-modal temporal perceptual biases depend on sensory experience and emerge during an early sensitive period.

neuroscience↗