***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background 10 Hz electroencephalographic ( EEG ) alpha rhythms correlate with memory performance . Alpha and memory decline in older people . We wished to test if alpha-like EEG activity contributes to memory formation . Flicker can elicit alpha-like EEG activity . We tested if alpha-frequency flicker enhances  memory in older people . Pariticpants aged 67–92 identified short words that followed 1 s of flicker at 9.0 Hz , 9.5 Hz , 10.0 Hz , 10.2 Hz , 10.5 Hz , 11.0 Hz , 11.5 Hz or 500 Hz . A few minutes later , we tested participants ' recognition of the words ( without flicker ) . Results Flicker frequencies close to 10 Hz ( 9.5–11.0 Hz ) facilitated the identification of the test words in older participants . The same flicker frequencies increased recognition of the words more than other frequencies ( 9.0 Hz , 11.5 Hz and 500 Hz ) , irrespective of age . Conclusion The frequency-specificity of flicker 's effects in our participants paralleled the power spectrum of EEG alpha in the general population . This indicates that alpha-like EEG activity may subserve memory processes . Flicker may be able to help memory problems in older people PURPOSE Transcranial alternating current stimulation ( tACS ) is a non-invasive stimulation technique for shaping neuroplastic processes and possibly entraining ongoing neural oscillations in humans . Despite the growing number of studies using tACS , we know little about the procedural sensations caused by stimulation . In order to fill this gap , we explored the cutaneous sensation and phosphene perception during tACS . METHODS Twenty healthy participants took part in a r and omized , single-blinded , sham-controlled study , where volunteers received short duration stimulation at 1.0 mA intensity between 2 to 250 Hz using the st and ard left motor cortex-contralateral supraorbital montage . We recorded the perception onset latency and the strength of the sensations assessed by visual rating scale as dependent variables . RESULTS We found that tACS evoked both cutaneous sensation and phosphene perception in a frequency-dependent manner . Our results show that the most perceptible procedural sensations were induced in the beta and gamma frequency range , especially at 20 Hz , whereas minimal procedural sensations were indicated in the ripple range ( 140 and 250 Hz ) . CONCLUSIONS We believe that our results provide a relevant insight into the procedural sensations caused by oscillatory currents , and will offer a basis for developing more sophisticated stimulation protocol s and study design s for future investigations Functional magnetic resonance imaging has been successfully used to map the activation in the lateral geniculate nucleus ( LGN ) in both hemispheres as well as the primary visual cortex ( V1 ) during a checkerboard visual stimulation . The average blood oxygenation level dependent ( BOLD ) change in LGN was less than that in V1 . However , the BOLD temporal responses were similar between LGN and V1 . The activation in the pulvinar nucleus during visual perception was also detected , and its activated location could be separated from LGN in 3D images . The LGN activation between intersubject and intrasubject multiple trials was compared . The results demonstrate that fMRI can reliably and robustly detect small subcortical nucleus activation in the human brain PURPOSE To assess the effect of intermittent photic stimulation ( IPS ) at a common activating frequency , i.e. 20Hz , on motor cortex excitability by means of transcranial magnetic stimulation ( TMS ) in photosensitive patients with idiopathic generalized epilepsy ( IGE ) . METHODS We studied 15 photosensitive IGE patients showing a photoparoxysmal response ( PPR ) to IPS at 20Hz . Nineteen normal subjects of similar age and sex acted as controls . After the resting motor threshold ( rMT ) was measured , we studied the corticomotor excitability in two conditions r and omly delivered , during IPS ( 5s ) at 20Hz and without IPS .  Motor evoked potentials ( MEPs ) were recorded from the right first dorsal interosseous muscle ( FDI ) . We determined the cortical silent period ( cSP ) , the short-latency intracortical inhibition ( SICI ) at the interstimulus interval ( ISI ) of 3 and 4ms and the intracortical facilitation ( ICF ) at ISIs of 12 and 14ms . Data were analyzed by means of rmANOVAs . RESULTS IPS at 20Hz is significantly shortening the cSP in normal subjects , while no significant changes were detected in patients . The rMT was significantly higher in patients than controls , as expected by the concurrent antiepileptic treatment . Other corticomotor excitability measures were unaffected . CONCLUSIONS We confirm that IPS has a weak influence on the motor cortical output in patients with IGE and PPR . The loss of the normal shortening of the cSP , otherwise present in healthy subjects in response to IPS , may have a possible protective nature Background Classically , studies adopting non-invasive transcranial electrical stimulation have placed greater importance on the position of the primary “ stimulating ” electrode than the secondary “ reference ” electrode . However , recent current density modeling suggests that ascribing a neutral role to the reference electrode may prove an inappropriate oversimplification . Hypothesis We set out to test the hypothesis that the behavioral effects of transcranial electrical stimulation are critically dependent on the position of the return ( “ reference ” ) electrode . Methods We examined the effect of transcranial alternating current stimulation ( sinusoidal waveform with no direct current offset at a peak-to-peak amplitude of 2000 μA and a frequency matched to each participant 's peak tremor frequency ) on physiological tremor in a group of healthy volunteers ( N = 12 ) . We implemented a sham-controlled experimental protocol where the position of the stimulating electrode remained fixed , overlying primary motor cortex , whilst the position of the return electrode varied between two cephalic ( fronto-orbital and contralateral primary motor cortex ) and two extracephalic ( ipsilateral and contralateral shoulder ) locations . We additionally controlled for the role of phosphenes in influencing motor output by assessing the response of tremor to photic stimulation , through self-reported phosphene ratings . Results Altering only the position of the return electrode had a profound behavioral effect : only the montage with extracephalic return contralateral to the primary stimulating electrode significantly entrained physiological tremor ( 15.9 % ± 6.1 % increase in phase stability , 1 S.E.M. ) . Photic stimulation also entrained tremor ( 11.7 % ± 5.1 % increase in phase stability ) . Furthermore , the effects of electrical stimulation are distinct from those produced from direct phosphene induction , in that the latter were only seen with the fronto-orbital montage that did not affect the tremor . Conclusion The behavioral effects of transcranial alternating current stimulation appear to be critically dependent on the position of the reference electrode , highlighting the importance of electrode montage when design ing experimental and therapeutic protocol 
    Output:
    
In this literature review , the importance of this issue is further illustrated by the fact that photic stimulation can have a direct impact on perceptual and cognitive performance .
This leaves open the possibility that peripheral photic stimulation can at least in part explain the central effects that are attributed to tACS .