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Are spatial frequency cues used for whisker-based active discrimination?

Georgieva P, Brugger D, Schwarz C - Front Behav Neurosci (2014)

Bottom Line: If they used spatial frequency cues, they would be able to optimize performance in a stimulus dependent way-by moving their whisker faster or slower across the texture surface, thereby shifting the frequency content of the neuronal signal toward an optimal working range for perception.The virtual grid mimicked discrete and repetitive whisker deflections generated by real objects (e.g., grove patterns) with single electrical microstimulation pulses delivered directly to the barrel cortex, and provided the critical advantage that stimuli could be controlled at highest precision.In striking contrast they could be easily trained to discriminate stimuli differing in electrical pulse amplitudes, a stimulus property that is not malleable by whisking.

View Article: PubMed Central - PubMed

Affiliation: Systems Neurophysiology, Werner Reichardt Center for Integrative Neuroscience, University Tübingen Tübingen, Germany ; Department for Cognitive Neurology, Hertie-Institute for Clinical Brain Research, University Tübingen Tübingen, Germany.

ABSTRACT
Rats are highly skilled in discriminating objects and textures by palpatory movements of their whiskers. If they used spatial frequency cues, they would be able to optimize performance in a stimulus dependent way-by moving their whisker faster or slower across the texture surface, thereby shifting the frequency content of the neuronal signal toward an optimal working range for perception. We tested this idea by measuring discrimination performance of head-fixed rats that were trained to actively sample from virtual grids. The virtual grid mimicked discrete and repetitive whisker deflections generated by real objects (e.g., grove patterns) with single electrical microstimulation pulses delivered directly to the barrel cortex, and provided the critical advantage that stimuli could be controlled at highest precision. Surprisingly, rats failed to use the spatial frequency cue for discrimination as a matter of course, and also failed to adapt whisking patterns in order to optimally exploit frequency differences. In striking contrast they could be easily trained to discriminate stimuli differing in electrical pulse amplitudes, a stimulus property that is not malleable by whisking. Intermingling these "easy-to-discriminate" discriminanda with others that solely offered frequency/positional cues, rats could be guided to base discrimination on frequency and/or position, albeit on a lower level of performance. Following this training, abolishment of electrical amplitude cues and reducing positional cues led to initial good performance which, however, was unstable and ran down to very low levels over the course of hundreds of trials. These results clearly demonstrate that frequency cues, while definitely perceived by rats, are of minor importance and they are not able to support consistent modulation of whisking patterns to optimize performance.

No MeSH data available.


Related in: MedlinePlus

Rats learn to discriminate ICMS amplitude but not spatial frequency. The plot shows the discrimination index (di, the difference between relative frequency of HIT and FA) for a task presenting virtual grids that differed in spatial frequency and range of grid bar positions (red dots, task 1) and a task that in addition offered differences in ICMS amplitude (blue dots, task 2). Rats 1–5 were trained exclusively with the first stimulus set and never learned the task. Rats 6, 7, after showing similar results on the first task were switched to task 2 and learned the task within several sessions (arrows). Rats 8–10 were trained only to task 2 and readily learned it. The icons depict the position of the virtual grid bars, gray: small ICMS amplitude, black: large ICMS amplitude.
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Figure 2: Rats learn to discriminate ICMS amplitude but not spatial frequency. The plot shows the discrimination index (di, the difference between relative frequency of HIT and FA) for a task presenting virtual grids that differed in spatial frequency and range of grid bar positions (red dots, task 1) and a task that in addition offered differences in ICMS amplitude (blue dots, task 2). Rats 1–5 were trained exclusively with the first stimulus set and never learned the task. Rats 6, 7, after showing similar results on the first task were switched to task 2 and learned the task within several sessions (arrows). Rats 8–10 were trained only to task 2 and readily learned it. The icons depict the position of the virtual grid bars, gray: small ICMS amplitude, black: large ICMS amplitude.

Mentions: The well habituated rats were trained on a Go/No Go discrimination task that required them to move their whisker to sample virtual grids (i.e., a series of ICMS pulses via one of the implanted microelectrodes, generated by issuing a single pulse every time the tracked whisker crossed a virtual grid point; Figure 1A), decide whether the stimulus predicted reward (Go) or not (No Go), and indicating this decision by either emitting a lick at the water spout (Go) or refraining to lick (No Go; Figure 1B). The training steps to acquire the capability to perform this task were as follows: in a first step all animals were conditioned to passively detect electrical stimulation (Butovas and Schwarz, 2007). A series of biphasic ICMS pulses (5–15 biphasic electrical pulses, 30–50 µA at 60 Hz; single pulse duration 500 µs) were generated using a programmable stimulator (STG4001; Multi Channel Systems MCS GmbH) and coincided with the delivery of a water drop at a spout positioned in front of the animal’s snout. Next, water delivery was made contingent on a correct lick after the ICMS pulse. After acquiring most of the rewards the number of ICMS pulses was decreased step-by-step until the animals detected well a single ICMS pulse. The lowest pulse amplitudes used in the present study to test discrimination ability were detected as single pulses by the animals at minimal correct response rates of 0.8. At this point a laser optical device (LOD, Metralight Inc., San Mateo, CA, USA) was used to track the C1 whisker (inserted in a light weight polyimide tube) at a distance of 2 cm from the face (Hentschke et al., 2006). The remaining whiskers were trimmed to 1 cm. The output of the LOD was monitored in real time and used to make the delivery of the ICMS pulse contingent to the crossing of a virtual grid point. In the beginning, the virtual grid point was located close to the resting position of the whisker, but in subsequent sessions, depending on the animals performance, it was placed farther and farther rostral to it. The rat was only rewarded for a successful movement eliciting an ICMS pulse followed by a lick, never for movement and licking alone. At this training level all rats generated large amplitude whisks (>30°). In the final step, the house light was used as an indicator that a trial could be initiated by whisking across the starting point (typically the whisker’s resting position). “House light off” indicated that the whisker was in the correct position behind the start point and that trial initiation was enabled. “House light on” signaled that the whisker was located rostral to the starting line and trial initiation was disabled. At this stage the single pulse stimulation was replaced by a virtual grid of three equally spaced virtual points. A stimulation pulse was delivered at each crossing of a virtual point in the protraction direction. In this way, a spatial virtual object—the 3-point grid—was translated into the temporal frequency of stimulation delivered to the barrel cortex (Figure 1A). After a 1 s sampling period, in which the animal was free to probe the virtual grid using movements of its choice (but was required to generate at least one full sweep across all three virtual grid points), a “window of opportunity” interval came on, signaled by switching on the house light. If the sampled stimulus predicted reward (S+), a lick in the window of opportunity yielded the delivery of a drop of water as reward. If the stimulus did not predict reward (S−), a lick in this period triggered a tone to signal the error followed by a light punishment in the form of a 2 s time out (Figure 1B). Subsequently, the next trial could be initiated any time given an interval of 200 ms had passed after the last lick. The rats were free to lick while sampling the virtual grid with no consequence. S+ and S− were presented in pseudo-random fashion. In all tests the overall ratio of S+/S− trails was 1:1. In some tests the group of S+ or S− trials were divided between many stimuli.


Are spatial frequency cues used for whisker-based active discrimination?

Georgieva P, Brugger D, Schwarz C - Front Behav Neurosci (2014)

Rats learn to discriminate ICMS amplitude but not spatial frequency. The plot shows the discrimination index (di, the difference between relative frequency of HIT and FA) for a task presenting virtual grids that differed in spatial frequency and range of grid bar positions (red dots, task 1) and a task that in addition offered differences in ICMS amplitude (blue dots, task 2). Rats 1–5 were trained exclusively with the first stimulus set and never learned the task. Rats 6, 7, after showing similar results on the first task were switched to task 2 and learned the task within several sessions (arrows). Rats 8–10 were trained only to task 2 and readily learned it. The icons depict the position of the virtual grid bars, gray: small ICMS amplitude, black: large ICMS amplitude.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4217502&req=5

Figure 2: Rats learn to discriminate ICMS amplitude but not spatial frequency. The plot shows the discrimination index (di, the difference between relative frequency of HIT and FA) for a task presenting virtual grids that differed in spatial frequency and range of grid bar positions (red dots, task 1) and a task that in addition offered differences in ICMS amplitude (blue dots, task 2). Rats 1–5 were trained exclusively with the first stimulus set and never learned the task. Rats 6, 7, after showing similar results on the first task were switched to task 2 and learned the task within several sessions (arrows). Rats 8–10 were trained only to task 2 and readily learned it. The icons depict the position of the virtual grid bars, gray: small ICMS amplitude, black: large ICMS amplitude.
Mentions: The well habituated rats were trained on a Go/No Go discrimination task that required them to move their whisker to sample virtual grids (i.e., a series of ICMS pulses via one of the implanted microelectrodes, generated by issuing a single pulse every time the tracked whisker crossed a virtual grid point; Figure 1A), decide whether the stimulus predicted reward (Go) or not (No Go), and indicating this decision by either emitting a lick at the water spout (Go) or refraining to lick (No Go; Figure 1B). The training steps to acquire the capability to perform this task were as follows: in a first step all animals were conditioned to passively detect electrical stimulation (Butovas and Schwarz, 2007). A series of biphasic ICMS pulses (5–15 biphasic electrical pulses, 30–50 µA at 60 Hz; single pulse duration 500 µs) were generated using a programmable stimulator (STG4001; Multi Channel Systems MCS GmbH) and coincided with the delivery of a water drop at a spout positioned in front of the animal’s snout. Next, water delivery was made contingent on a correct lick after the ICMS pulse. After acquiring most of the rewards the number of ICMS pulses was decreased step-by-step until the animals detected well a single ICMS pulse. The lowest pulse amplitudes used in the present study to test discrimination ability were detected as single pulses by the animals at minimal correct response rates of 0.8. At this point a laser optical device (LOD, Metralight Inc., San Mateo, CA, USA) was used to track the C1 whisker (inserted in a light weight polyimide tube) at a distance of 2 cm from the face (Hentschke et al., 2006). The remaining whiskers were trimmed to 1 cm. The output of the LOD was monitored in real time and used to make the delivery of the ICMS pulse contingent to the crossing of a virtual grid point. In the beginning, the virtual grid point was located close to the resting position of the whisker, but in subsequent sessions, depending on the animals performance, it was placed farther and farther rostral to it. The rat was only rewarded for a successful movement eliciting an ICMS pulse followed by a lick, never for movement and licking alone. At this training level all rats generated large amplitude whisks (>30°). In the final step, the house light was used as an indicator that a trial could be initiated by whisking across the starting point (typically the whisker’s resting position). “House light off” indicated that the whisker was in the correct position behind the start point and that trial initiation was enabled. “House light on” signaled that the whisker was located rostral to the starting line and trial initiation was disabled. At this stage the single pulse stimulation was replaced by a virtual grid of three equally spaced virtual points. A stimulation pulse was delivered at each crossing of a virtual point in the protraction direction. In this way, a spatial virtual object—the 3-point grid—was translated into the temporal frequency of stimulation delivered to the barrel cortex (Figure 1A). After a 1 s sampling period, in which the animal was free to probe the virtual grid using movements of its choice (but was required to generate at least one full sweep across all three virtual grid points), a “window of opportunity” interval came on, signaled by switching on the house light. If the sampled stimulus predicted reward (S+), a lick in the window of opportunity yielded the delivery of a drop of water as reward. If the stimulus did not predict reward (S−), a lick in this period triggered a tone to signal the error followed by a light punishment in the form of a 2 s time out (Figure 1B). Subsequently, the next trial could be initiated any time given an interval of 200 ms had passed after the last lick. The rats were free to lick while sampling the virtual grid with no consequence. S+ and S− were presented in pseudo-random fashion. In all tests the overall ratio of S+/S− trails was 1:1. In some tests the group of S+ or S− trials were divided between many stimuli.

Bottom Line: If they used spatial frequency cues, they would be able to optimize performance in a stimulus dependent way-by moving their whisker faster or slower across the texture surface, thereby shifting the frequency content of the neuronal signal toward an optimal working range for perception.The virtual grid mimicked discrete and repetitive whisker deflections generated by real objects (e.g., grove patterns) with single electrical microstimulation pulses delivered directly to the barrel cortex, and provided the critical advantage that stimuli could be controlled at highest precision.In striking contrast they could be easily trained to discriminate stimuli differing in electrical pulse amplitudes, a stimulus property that is not malleable by whisking.

View Article: PubMed Central - PubMed

Affiliation: Systems Neurophysiology, Werner Reichardt Center for Integrative Neuroscience, University Tübingen Tübingen, Germany ; Department for Cognitive Neurology, Hertie-Institute for Clinical Brain Research, University Tübingen Tübingen, Germany.

ABSTRACT
Rats are highly skilled in discriminating objects and textures by palpatory movements of their whiskers. If they used spatial frequency cues, they would be able to optimize performance in a stimulus dependent way-by moving their whisker faster or slower across the texture surface, thereby shifting the frequency content of the neuronal signal toward an optimal working range for perception. We tested this idea by measuring discrimination performance of head-fixed rats that were trained to actively sample from virtual grids. The virtual grid mimicked discrete and repetitive whisker deflections generated by real objects (e.g., grove patterns) with single electrical microstimulation pulses delivered directly to the barrel cortex, and provided the critical advantage that stimuli could be controlled at highest precision. Surprisingly, rats failed to use the spatial frequency cue for discrimination as a matter of course, and also failed to adapt whisking patterns in order to optimally exploit frequency differences. In striking contrast they could be easily trained to discriminate stimuli differing in electrical pulse amplitudes, a stimulus property that is not malleable by whisking. Intermingling these "easy-to-discriminate" discriminanda with others that solely offered frequency/positional cues, rats could be guided to base discrimination on frequency and/or position, albeit on a lower level of performance. Following this training, abolishment of electrical amplitude cues and reducing positional cues led to initial good performance which, however, was unstable and ran down to very low levels over the course of hundreds of trials. These results clearly demonstrate that frequency cues, while definitely perceived by rats, are of minor importance and they are not able to support consistent modulation of whisking patterns to optimize performance.

No MeSH data available.


Related in: MedlinePlus