Ultra Compact Nanoporous Platinum Coating Improves Neural Recording

Neural electrodes are key tools for achieving a successful brain-computer interface and the electrodes should be small to minimize damage to neural tissue and obtain good spatial selectivity such as single unit recording. Here we show conventional platinum/tungsten neural probes can be coated with nanoporous Pt. Thanks to nanoporous Pt with the extremely small and uniform pores, L-2-ePt, the electrode impedance could be reduced by more than 2 orders of magnitude while the apparent area was almost the same. L-2-ePt coating enhanced neuronal recording of local field potential in monkeys, leading to facilitating implanted electrical devices in the nervous system.Peer reviewe

P3-9: Roles of Subthreshold LFP Induced by Receptive Field Surround for Response Modulation in Monkey V1

A focal stimulus outside the receptive field robustly induces LFP change, while the same stimulus evokes no spike activity. We determined how this subthreshold LFP change interacted with spike response to the RF stimulus. Specifically, we sequentially presented two identical Gabor stimuli with a variable stimulus onset asynchrony (SOA); the first one (S1) was presented outside RF inducing a subthreshold LFP change, and the second one (S2) was subsequently presented within RF generating a spiking response. This enabled us to manipulate the temporal relation between subthreshold LFP and evoked spike activity and to determine whether subthreshold LFP contributed to modulation of spike activity in a SOA-dependent manner. We found that the subthreshold LFP propagated a considerably long distance, estimated to be more than 10 mm of cortical distance. The cross-correlation between the time course of subthreshold LFP and the pattern of SOA-dependency of spike activity was significant. These results indicate that signal integration is farther beyond the RF than previously estimated based on spike-triggered average, and suggest that subthreshold LFP modulate spike activity in a SOA-dependent manner

Modulation of V1 spike response by temporal interval of spatiotemporal stimulus sequence.

The spike activity of single neurons of the primary visual cortex (V1) becomes more selective and reliable in response to wide-field natural scenes compared to smaller stimuli confined to the classical receptive field (RF). However, it is largely unknown what aspects of natural scenes increase the selectivity of V1 neurons. One hypothesis is that modulation by surround interaction is highly sensitive to small changes in spatiotemporal aspects of RF surround. Such a fine-tuned modulation would enable single neurons to hold information about spatiotemporal sequences of oriented stimuli, which extends the role of V1 neurons as a simple spatiotemporal filter confined to the RF. In the current study, we examined the hypothesis in the V1 of awake behaving monkeys, by testing whether the spike response of single V1 neurons is modulated by temporal interval of spatiotemporal stimulus sequence encompassing inside and outside the RF. We used two identical Gabor stimuli that were sequentially presented with a variable stimulus onset asynchrony (SOA): the preceding one (S1) outside the RF and the following one (S2) in the RF. This stimulus configuration enabled us to examine the spatiotemporal selectivity of response modulation from a focal surround region. Although S1 alone did not evoke spike responses, visual response to S2 was modulated for SOA in the range of tens of milliseconds. These results suggest that V1 neurons participate in processing spatiotemporal sequences of oriented stimuli extending outside the RF

Response Modulation of V1 Neurons by Spatiotemporal Sequence of Oriented Stimuli

Spike activity of V1 neurons in response to natural scene (Vinje and Gallant, 2002; Montemurro et al., 2008; Haider et al., 2010) is surprisingly consistent across repeated trials. While it is clear that these responses are not explained by classical receptive field (cRF) properties, it is not known how surround interaction increases the selectivity of V1 response. Put more generally, we do not completely understand the mapping rules between elementary features of visual scene and V1 activity. In the current study we examined the possibility that V1 neurons are selective for spatiotemporal sequence of oriented stimuli. We will describe a novel response property of monkey V1 neurons that visual response was modulated depending on the stimulus onset asynchrony (SOA) in the range of tens of milliseconds between two sequentially presented Gabor stimuli. The preceding stimulus (S1) was presented outside cRF and the following one (S2) inside cRF. S1 alone did not evoke spike response but modulated cell's response to S2. Spike response to S2 was not constant across SOA, and the SOA associated with maximal response modulation varied with the position of S1. These results suggest that V1 neurons are selective for spatiotemporal sequence of oriented stimuli based on surround interaction

Distinct Hippocampal Oscillation Dynamics in Trace Eyeblink Conditioning Task for Retrieval and Consolidation of Associations

Trace eyeblink conditioning (TEBC) has been widely used to study associative learning in both animals and humans. In this paradigm, conditioned responses (CRs) to conditioned stimuli (CS) serve as a measure for retrieving learned associations between the CS and the unconditioned stimuli (US) within a trial. Memory consolidation, that is, learning over time, can be quantified as an increase in the proportion of CRs across training sessions. However, how hippocampal oscillations differentiate between successful memory retrieval within a session and consolidation across TEBC training sessions remains unknown. To address this question, we recorded local field potentials (LFPs) from the rat dorsal hippocampus during TEBC and investigated hippocampal oscillation dynamics associated with these two functions. We show that transient broadband responses to the CS were correlated with memory consolidation, as indexed by an increase in CRs across TEBC sessions. In contrast, induced alpha (8–10 Hz) and beta (16–20 Hz) band responses were correlated with the successful retrieval of the CS–US association within a session, as indexed by the difference in trials with and without CR.peerReviewe

Pattern of modulation for collinear (A–D) and parallel (E–H) S1 conditions.

<p>(A) Combined time course of SOA-dependent significant facilitation (p<0.05) from 2288 SOA conditions of 208 collinear S1 stimuli. Normalized frequency of significant epoch is color-coded according to the color map shown on the right. Out of 2288, 208 (9.09%) SOA conditions included more than one temporal epoch with significant facilitation. (B) Time course of significant suppression combined from the same collinear S1 configurations. In 611 of 2288 (26.70%) SOA conditions, more than one temporal epoch showed significant suppression. (C) Normalized marginal frequency of significant facilitation from A (red) and suppression from B (blue) against peristimulus time. (D) Normalized marginal frequency of significant facilitation (A, red) and suppression (B, blue) during the poststimulus time period from 0 to 300 ms against SOA. Normallized marginal frequency was derived from marginal sum divided by the number of data points. (E–H) Similar plots as A–D combined from 572 SOA conditions of 52 parallel configurations. Out of 572 SOA conditions, 96 (16.78%) and 71 (12.41%) SOA groups showed significant facilitation and suppression, respectively. Thus, suppression was relatively common with collinear S1, and the relative ratio of facilitative modulation was higher with the parallel configuration. This was true even after the distance between S1 and S2 was taken into account (by subdividing S1 configuration conditions into two distance groups, one or two RF diameter away from RF center). Note that suppressive modulation was concentrated at around 100 ms after S2 onset time (C, G), whereas facilitative modulation was relatively more dispersed and dominant after around 200 ms after S2 onset, especially in the parallel configuration. Also note that collinear S1 tended to suppress at short SOA and facilitate at long SOA (D), whereas this dissociation was relatively weak with parallel S1 (H).</p

Scatter plot of selectivity index and cortical distance.

<p>Each dot represents selectivity index (SI) for each stimulus condition and anatomical distance between the centers of S1 and S2 for that condition. Mariginal histograms are also shown. The cortical distance was estimated from the cortical magnification factor <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047543#pone.0047543-Horton1" target="_blank">[31]</a>. Data are combined single and multiple unit data obtained from 227 stimulus conditions (i.e., S1 positions) for 105 recording sites in 2 monkeys. Black dots and bars indicate significant <i>SIs</i> (69 of 227 cases, 30.40%, p<0.05), as evaluated with a bootstrapping method. The proportion was also consistent for single units alone (23 of 92 stimulus conditions, 25%) and multiple unit activitiy (46 of 135 stimulus conditions, 34.07%).The proportion of significant <i>SI</i> decreased with the cortical distance between S1 and S2.</p

Summary of stimulus conditions.

<p>Ipsilateral S1: S1 was presented in the hemifield ipsilateral to RF; Contralateral S1: S1 was presented in the hemifield contralateral to RF. The numbers in parentheses refer to stimulus conditions in which the response to S2 alone was not tested.</p