Area 21a of cat visual cortex strongly modulates neuronal activities in the superior colliculus

We have examined the influence of cortico-tectal projections from one of the pattern-processing extrastriate visual cortical areas, area 21a, on the responses to visual stimuli of single neurones in the superior colliculi of adult cats. For this purpose area 21a was briefly inactivated by cooling to 10 °C using a Peltier device. Responses to visual stimuli before and during cooling as well as after rewarming ipsilateral area 21a were compared. In addition, in a subpopulation of collicular neurones we have studied the effects of reversible inactivation of ipsilateral striate cortex (area 17, area V1). When area 21a was cooled, the temperature of area 17 was kept at 36 °C and vice versa. In the majority of cases (41/65; 63 %), irrespective of the velocity response profiles of collicular neurones, inactivation of area 21a resulted in a significant decrease in magnitude of responses of neurones in the ipsilateral colliculus and only in a small proportion of cells (2/65; 3.1 %) was there a significant increase in the magnitude of responses. Inactivation of area 21a resulted in significant changes in the magnitude of responses of collicular cells located not only in the retino-recipient layers but also in the stratum griseum intermediale. In most cases, reversible inactivation of area 17 resulted in a greater reduction in the magnitude of responses of collicular cells than inactivation of area 21a. Reversible inactivation of area 21a also affected the direction selectivity indices and length tuning of most collicular cells tested

Influence of serotonin receptor 2A His452Tyr polymorphism on brain temporal structures: a volumetric MR study

Serotonin (5-HT) receptors 2A are expressed in brain regions involved in memory and learning processes. Recently, a functional single nucleotide polymorphism in the 5-HT2A receptor gene leading to an amino-acid substitution at residue 452 (His452Tyr) has been involved in memory performance, persons with the rare 452Tyr allele showing poorer memory performance compared to His452His subjects. To investigate a putative structural effect of this polymorphism on temporal areas typically involved in memory processes, we performed voxel-based morphometry (VBM) and region-of-interest (ROI) volumetric analysis on high-resolution magnetic resonance images in 15 carriers and 61 noncarriers of the 452Tyr allele. ROI volumetric analysis showed a significant reduction of the fractional volume of the temporal white matter in 452Tyr carriers (0.67+/-0.07 vs 0.73+/-0.08; P=0.007). VBM confirmed this finding and in addition showed reduced grey matter in the left hippocampus, left inferior temporal gyrus, and bilaterally in the middle and superior temporal gyrus. A possible effect on synaptic plasticity or neurodevelopment might explain the influence of the His452Tyr polymorphism on temporal brain structures, and this might be the basis for poorer memory performance in 452Tyr carriers. These findings should be considered preliminary and future replication is needed