[Show abstract][Hide abstract] ABSTRACT: In our very recent article, we have reviewed the wide range of TPM side ef-fects on vision of 84 patients culled from the literature 2 . As far as we are aware in terms of TPM related visual illusions, five other cases 3-5 are described in the literature, and the authors of the above report have added the sixth one 1 . It is important to underline that the authors reported a positive dechallenge test that corroborates a causal relationship between TPM and such an adverse effect 1,6 . Nevertheless, in their final conclu-sion on the etiology of such an association, they stated that "because it may occur in the aura of migraines, these visual illusions are likely to be a result of the migraine" 1 . Indeed, one of the leading TPM indications is prevention of migraine at-tacks and herein comes the uncertainty of whether illusions are linked to migraine or to TPM use. To clarify, firstly, we need to know if TPM associated vi-sual illusions are only observed in migraine consumers. In other words, is there any similar report on a non-migraineur? The authors in their literature review noted two studies re-porting illusions in four TPM consumers who were all mi-graineurs (two cases with palinopsia 3 and two with Alice-in-wonderland syndrome 3,4). Notwithstanding this review, the answer of the above question is positive. Fontenelle, in 2008 5 , described palinopsia in a non-migraineur taking TPM for in-somnia and impulsive behaviors. Secondly, we need to know if all of the aforementioned four migraineurs had had history of migraine aura before con-sumption of TPM. The answer is negative. Only one of them had aura, and in this case no clear temporal relationship was observed between migraine attacks and visual illusions 3 . Thirdly, it would be rational to adhere to the results of dechallenge and rechallenge tests in this regard. In all ofthe aforementioned four migraine patients positive dechal-lenge tests were reported alike what the authors found 3,4 . Moreover, three of these cases were examined by rechal-lenge tests giving positive results (two palinopsia 3 and one Alice-in-wonderland syndrome 4 patients). Engagingly, two of them showed "a clear dose related association with the use of topiramate and the elicitation of palinopsia" 3 . It is to be noted that rechallenge tests are reputed for being almost the gold standard test in establishing or excluding the etiol-ogy of adverse effects ascribed to drugs 6 . In conclusion, we believe that, along with other drugs, TPM use should be added to the differential diagnosis of visual illusions in migraineurs or non-migraineurs either. Nonetheless, we endorse the notion that the underlying mi-graine in a vast proportion of TPM consumers can substan-tially predispose them to these symptoms 1,3,4 . 1. Cerqueira AC, Nardi AE. Metamorphopsia associated with topiramate for migraine prevention. Arq Neuropsiquiatr 2012;70:231-232.
Arquivos de Neuro-Psiquiatria 09/2012; · 0.84 Impact Factor
"Interestingly , these and other antidepressants are known to increase extracellular levels of serotonin (Boyer and Shannon 2005), lending credence to the idea that similar visual disturbances due to LSD may arise from modulation of serotonin. Antiepileptic drugs like topiramate can also lead to visual trails described similarly to those seen in HPPD (Fontenelle 2008). Finally, Alzheimers patients have been recently reported the experience of akinetopsia, where moving objects are perceived as a series of stills (Tsai and Mendez 2009). "
[Show abstract][Hide abstract] ABSTRACT: We study the spatiotemporal dynamics of neuronal networks with spike frequency adaptation. In particular, we compare the effects of adaptation being either a linear or nonlinear function of neural activity. We find that altering parameters controlling the strength of synaptic connections in the network can lead to spatially structured activity suggestive of symptoms of hallucinogen persisting perception disorder (HPPD). First, we study how both networks track spatially homogeneous flickering stimuli, and find input is encoded as continuous at lower flicker frequencies when the network's synapses exhibit more net excitation. Mainly, we study instabilities of stimulus-driven traveling pulse solutions, representative of visual trailing phenomena common to HPPD patients. Visual trails are reported as discrete afterimages in the wake of a moving input. Thus, we analyze several solutions arising in response to moving inputs in both networks: an ON state, stimulus-locked pulses, and traveling breathers. We find traveling breathers can arise in both networks when an input moves beyond a critical speed. These possible neural substrates of visual trails occur at slower speeds when the modulation of synaptic connectivity is increased.
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