BEGIN:VCALENDAR
VERSION:2.0
PRODID:icalendar-ruby
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:Europe/Vienna
BEGIN:DAYLIGHT
DTSTART:20210328T030000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
TZNAME:CEST
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:20201025T020000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:CET
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:20260404T151022Z
UID:1605276000@ist.ac.at
DTSTART:20201113T150000
DTEND:20201113T160000
DESCRIPTION:Speaker: Tatjana Tchumatchenko\nhosted by Everton Agnes\nAbstra
 ct: Neurons in the primary visual cortex (V1) encode the orientation and c
 ontrast of visual stimuli through changes in firing rate (Hubel and Wiesel
 \, 1962). Their activity typically peaks at a preferred orientation and de
 cays to zero at the orientations that are orthogonal to the preferred. Thi
 s activity pattern is re-scaled by contrast but its shape is preserved\, a
  phenomenon known as contrast invariance. Contrast-invariant selectivity i
 s also observed at the population level in V1 (Carandini and Sengpiel\, 20
 04). The mechanisms supporting the emergence of contrast-invariance at the
  population level remain unclear. How does the activity of different neuro
 ns with diverse orientation selectivity and non-linear contrast sensitivit
 y combine to give rise to contrast-invariant population selectivity? Theor
 etical studies have shown that in the balance limit\, the properties of si
 ngle-neurons do not determine the population activity (van Vreeswijk and S
 ompolinsky\, 1996). Instead\, the synaptic dynamics (Mongillo et al.\, 201
 2) as well as the intracortical connectivity (Rosenbaum and Doiron\, 2014)
  shape the population activity in balanced networks.  We report that shor
 t-term plasticity can change the synaptic strength between neurons as a fu
 nction of the presynaptic activity\, which in turns modifies the populatio
 n response to a stimulus. Thus\, the same circuit can process a stimulus i
 n different ways –linearly\, sublinearly\, supralinearly – depending o
 n the properties of the synapses. We found that balanced networks with exc
 itatory to excitatory short-term synaptic plasticity cannot be contrast-in
 variant. Instead\, short-term plasticity modifies the network selectivity 
 such that the tuning curves are narrower (broader) for increasing contrast
  if synapses are facilitating (depressing).Based on these results\, we won
 dered whether balanced networks with plastic synapses (other than short-te
 rm) can support the emergence of contrast-invariant selectivity. Mathemati
 cally\, we found that the only synaptic transformation that supports perfe
 ct contrast invariance in balanced networks is a power-law release of neur
 otransmitter as a function of the presynaptic firing rate (in the excitato
 ry to excitatory and in the excitatory to inhibitory neurons). We validate
  this finding using spiking network simulations\, where we report contrast
 -invariant tuning curves when synapses release the neurotransmitter follow
 ing a power- law function of the presynaptic firing rate. In summary\, we 
 show that synaptic plasticity controls the type of non-linear network resp
 onse to  stimulus contrast and that it can be a potential mechanism media
 ting the emergence of contrast invariance in balanced networks with orient
 ation-dependent connectivity. Our results therefore connect the physiology
  of individual synapses to the network level and may help understand the e
 stablishment of contrast-invariant selectivity.
LOCATION:Online\, ISTA
ORGANIZER:
SUMMARY:Tatjana Tchumatchenko: The emergence of contrast invariance in cort
 ical circuits
URL:https://talks-calendar.ista.ac.at/events/2942
END:VEVENT
END:VCALENDAR