Adaptive behavior of neighboring neurons during adaptation-induced plasticity of orientation tuning in V1

<p>Abstract</p> <p>Background</p> <p>Sensory neurons display transient changes of their response properties following prolonged exposure to an appropriate stimulus (adaptation). In adult cat primary visual cortex, orientation-selective neurons shift their preferred orientation after being adapted to a non-preferred orientation. The direction of those shifts, towards (attractive) or away (repulsive) from the adapter depends mostly on adaptation duration. How the adaptive behavior of a neuron is related to that of its neighbors remains unclear.</p> <p>Results</p> <p>Here we show that in most cases (75%), cells shift their preferred orientation in the same direction as their neighbors. We also found that cells shifting preferred orientation differently from their neighbors (25%) display three interesting properties: (i) larger variance of absolute shift amplitude, (ii) wider tuning bandwidth and (iii) larger range of preferred orientations among the cluster of cells. Several response properties of V1 neurons depend on their location within the cortical orientation map. Our results suggest that recording sites with both attractive and repulsive shifts following adaptation may be located in close proximity to iso-orientation domain boundaries or pinwheel centers. Indeed, those regions have a more diverse orientation distribution of local inputs that could account for the three properties above. On the other hand, sites with all cells shifting their preferred orientation in the same direction could be located within iso-orientation domains.</p> <p>Conclusions</p> <p>Our results suggest that the direction and amplitude of orientation preference shifts in V1 depend on location within the orientation map. This anisotropy of adaptation-induced plasticity, comparable to that of the visual cortex itself, could have important implications for our understanding of visual adaptation at the psychophysical level.</p

Synchrony between orientation-selective neurons is modulated during adaptation-induced plasticity in cat visual cortex

<p>Abstract</p> <p>Background</p> <p>Visual neurons respond essentially to luminance variations occurring within their receptive fields. In primary visual cortex, each neuron is a filter for stimulus features such as orientation, motion direction and velocity, with the appropriate combination of features eliciting maximal firing rate. Temporal correlation of spike trains was proposed as a potential code for linking the neuronal responses evoked by various features of a same object. In the present study, synchrony strength was measured between cells following an adaptation protocol (prolonged exposure to a non-preferred stimulus) which induce plasticity of neurons' orientation preference.</p> <p>Results</p> <p>Multi-unit activity from area 17 of anesthetized adult cats was recorded. Single cells were sorted out and (1) orientation tuning curves were measured before and following 12 min adaptation and 60 min after adaptation (2) pairwise synchrony was measured by an index that was normalized in relation to the cells' firing rate. We first observed that the prolonged presentation of a non-preferred stimulus produces attractive (58%) and repulsive (42%) shifts of cell's tuning curves. It follows that the adaptation-induced plasticity leads to changes in preferred orientation difference, i.e. increase or decrease in tuning properties between neurons. We report here that, after adaptation, the neuron pairs that shared closer tuning properties display a significant increase of synchronization. Recovery from adaptation was accompanied by a return to the initial synchrony level.</p> <p>Conclusion</p> <p>We conclude that synchrony reflects the similarity in neurons' response properties, and varies accordingly when these properties change.</p

Visual Cells Remember Earlier Applied Target: Plasticity of Orientation Selectivity

BACKGROUND: A canonical proposition states that, in mature brain, neurons responsive to sensory stimuli are tuned to specific properties installed shortly after birth. It is amply demonstrated that that neurons in adult visual cortex of cats are orientation-selective that is they respond with the highest firing rates to preferred oriented stimuli. METHODOLOGY/PRINCIPAL FINDINGS: In anesthetized cats, prepared in a conventional fashion for single cell recordings, the present investigation shows that presenting a stimulus uninterruptedly at a non-preferred orientation for twelve minutes induces changes in orientation preference. Across all conditions orientation tuning curves were investigated using a trial by trial method. Contrary to what has been previously reported with shorter adaptation duration, twelve minutes of adaptation induces mostly attractive shifts, i.e. toward the adapter. After a recovery period allowing neurons to restore their original orientation tuning curves, we carried out a second adaptation which produced three major results: (1) more frequent attractive shifts, (2) an increase of their magnitude, and (3) an additional enhancement of responses at the new or acquired preferred orientation. Additionally, we also show that the direction of shifts depends on the duration of the adaptation: shorter adaptation in most cases produces repulsive shifts, whereas adaptation exceeding nine minutes results in attractive shifts, in the same unit. Consequently, shifts in preferred orientation depend on the duration of adaptation. CONCLUSION/SIGNIFICANCE: The supplementary response improvements indicate that neurons in area 17 keep a memory trace of the previous stimulus properties, thereby upgrading cellular performance. It also highlights the dynamic nature of basic neuronal properties in adult cortex since repeated adaptations modified both the orientation tuning selectivity and the response strength to the preferred orientation. These enhanced neuronal responses suggest that the range of neuronal plasticity available to the visual system is broader than anticipated

Typical example of shift in orientation preference and response modulations.

<p>A: The first 12 min adaptation displaces the preferred orientation of the cell by 15.5° toward the adapting stimulus. The head arrow indicates the non-preferred adapting stimulus. Following a recovery period of 60 min, the cell recovered its control preferred orientation at 9.0°. Adaptation II produces an identical attractive shift of 15.1°. B, C and D: Histograms shows the response modulations at the control preferred orientation, the new preferred orientation after adaptations and the baseline level (θ = 90°), respectively. At the control preferred orientation, the mean firing rate of cell decrease after adaptation I (<i>t</i>-test, p<0.001) and returned to control level in 60 min. In parallel, the mean firing rate increase by 27% at the new preferred orientation (<i>t</i>-test, p<0.0001). Following recovery, the firing rate further increases: 48% in comparison to adaptation I (<i>t</i>-test, p<0.0001). Baseline level remains unchanged across conditions. E and F: Peri-stimulus time histograms (PSTH) are illustrated for the neuron responding to orientations in C and D, respectively. Blue curves; control condition, red curves; adaptation I, black curves; adaptation II.</p

Adaptation-induced plasticity of orientation tuning in a population of 69 neurons.

<p>A: Scatter plot showing the amplitude of shifts in preferred orientation after adaptation as a function of the absolute difference between the control preferred orientation and the adapting orientation. Black dots represent shifts orientation preference following adaptation I and gray dots following adaptation II. Positive values designate attractive shifts and negative values designate repulsive shifts. The majority of cells 80% (55/69) displayed significant shifts in orientation preference. Dashed lines represent the significance level. Adaptation I induced mostly significant attractive shifts 74% (41/55) and 26% of significant repulsive shifts (14/55). Overall, the mean attractive shift is 15.7°±1.8°, while the average repulsive shifts is 15.6°±2.9° (red dots; errors bars are SEM). Adaptation II induced more attractive shifts 84% (46/55) than repulsive ones 16% (11/55). The magnitude of the attractive shifts significantly increased to 19.5°±1.3° (Mann Whitney test p<0.01) whereas the mean repulsive shits slightly diminished to 13.6°±2.0° (amber dots; errors bars are SEM). B: Neurons displaying significant (<i>t</i>-test, p<0.05) and non-significant (<i>t</i>-test, p>0.05) changes in orientation preference are compared regardless of shifts direction (shifts pooled). The mean shift amplitude of orientation is 15.4°+/−1.3° whereas non-significant shifts average 2.6°+/−0.4°. Insert: The jitter in preferred orientations is unchanged following adaptation, prior to adaptation: 2.2°+/−0.02°; following adaptation: 2.4°+/−0.02° I (errors bars are SEM). The histograms suggest that the peak orientation is almost invariant.</p

(A) Scatter plot showing the amplitude of shifts in preferred orientation after adaptation as a function of the absolute difference between the control preferred orientation and the adapting orientation

Positive values (black dots) designate attractive shifts (n = 42) and negative values (grey dots) designate repulsive shifts (n = 30). The dashed lines in black and grey indicate the mean amplitude for attractive (17.3°) and repulsive (13.5°) shifts, respectively. (B) Scatter plot displaying the signal-to-noise (S/N) ratio of neuronal spikes' waveforms in the control condition as a function of the absolute shift amplitude (black dots indicate attractive shifts, whereas grey dots indicate repulsive shifts). Data are equally distributed around the S/N ratio mean values for both attractive (black dashed line) and repulsive shifts (grey dashed line). This distribution shows that shifts in orientation preference are unrelated to the S/N ratio (r < 0.1 regardless the direction of the shift). (C) Histograms showing the modulation of mean firing rate between , and conditions (error bars are SEM). Left: following the adaptation, a significant decrease of the firing rate is observed for the initial preferred orientation; paired sample two-tailed -test, < 0.001. Middle: in parallel, a significant increase of the response is observed for the newly acquired preferred orientation (attractive and repulsive shifts pooled together); paired sample two-tailed -test, < 0.01. Right: there are no significant changes in the response of far flank orientations (baseline); paired sample two-tailed -test, > 0.1. In all cases, recoveries are shown 60 minutes after the adaptation ended.<p><b>Copyright information:</b></p><p>Taken from "Synchrony between orientation-selective neurons is modulated during adaptation-induced plasticity in cat visual cortex"</p><p>http://www.biomedcentral.com/1471-2202/9/60</p><p>BMC Neuroscience 2008;9():60-60.</p><p>Published online 3 Jul 2008</p><p>PMCID:PMC2481260.</p><p></p