Tonic response types in three regions of the auditory forebrain of trained monkeys.

<p>(A) Time course of the normalized firing rate of 82 multiunits in RAC whose firing rate slowly decreased during the waiting period. The two purple vertical bars mark the time windows that were used to select these multiunits. The vertical dashed line marks the onset of the 4th tone. The black curve was calculated from trials in which the monkey correctly responded to the downstep after the presentation of the intermittent tones. The relative frequency of response times is shown in the lower right histogram (black bars). The red curve was calculated from trials in which the monkeys incorrectly responded to the upstep. The relative frequency of incorrect response times is shown in the lower right histogram (red bars). The shaded curves reflect the standard errors of the mean for each of the two curves. The increased firing about 2000 to 2800 ms before sequence onset is related to bar grasping and to the onset of the cue light. Firing before bar grasping (marked by the arrow) is dispersed because bar grasps occurred after variable reaction times after the cue-light. (B) Results of 127 multiunits in LAC whose firing rate decreased during the waiting period. (C) Results of 26 multiunits in MGB whose firing rate decreased during the waiting period. (D) Results of 61 multiunits in LAC whose firing rate increased during the waiting period. (E) Results of 19 multiunits in MGB whose firing rate decreased during the initial tones of the sequence. (F) Results of 72 multiunits in LAC whose firing rate increased during the initial tones of the sequence. (G) Results of 11 multiunits in MGB whose firing rate increased during the intermittent tones of the sequence. (H) Results of 89 multiunits in LAC whose firing rate decreased during the intermittent tones of the sequence.</p

Similar discrimination of tone steps in correct and error trials in three regions of the auditory forebrain of trained monkeys.

<p>(A) The four histograms show the distributions of average ranks of phasic response increases calculated from 34 multiunits in RAC for upsteps (red curves) and downsteps (green curves), in trials with correct (solid lines) and incorrect behavioral responses (dashed lines). For each multiunit, the phasic response increases were rank ordered, with a rank of 1 assigned to the smallest increase and a rank of 4 assigned to the greatest increase. For further details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#sec002" target="_blank">Methods</a>. (B) Results for 20 multiunits in MGB. (C) Results for 36 multiunits in LAC.</p

Phasic responses to three classes of tone steps in the auditory forebrain.

<p>(A) Multiunit activity recorded in right auditory cortex (RAC). In the raster display, the dots in each horizontal raster line indicate when the multiunit fired spikes relative to the 2nd tone of different exemplars of downsteps (green), upsteps (red), and frequency repeats (blue). Small tone steps (0.5 octaves) are depicted by pale dots, large tone steps (1 octave) by bold dots. Gray bars underneath the abscissas indicate the 1st and the 2nd tone of the tone step. The left ordinate indicates the trial number. The right ordinate indicates the frequency of the 2nd tone of the tone steps, i. e., the trigger tone. The post stimulus time histograms underneath the rastergrams show the time courses of the normalized spike rate averaged across all downsteps, all upsteps, and all frequency repeats. The inset shows the frequency response area of this multiunit. (B) Multiunit activity recorded in medial geniculate body (MGB).</p

Time courses of choice probabilities after sequence onset in three regions of the auditory forebrain.

<p>(A) The thick lines show mean CPs of 239 multiunits recorded in RAC. The thin lines show mean CPs of 82 multiunits recorded in RAC whose firing rate slowly decreased during the waiting period (cp. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#pone.0186556.g008" target="_blank">Fig 8A</a>). The two green curves represent comparisons between hits and misses. The two red curves represent comparisons between false alarms and correct rejections. The shaded curves reflect the standard errors of the mean for each of the four curves. Note that for the latter comparisons, CPs of two more 200-ms time windows could be shown. The dots represent CPs significantly different from 0.5 (t-test, p < 0.001). The vertical dashed line marks the 4th tone. (B) CPs of all 50 multiunits recorded in MGB (thick lines) and of 26 multiunits in MGB whose firing rate slowly decreased during the waiting period (thin lines; cp. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#pone.0186556.g008" target="_blank">Fig 8C</a>). (C) CPs of all 309 multiunits recorded in LAC (thick lines) and of 127 multiunits in LAC whose firing rate slowly decreased during the waiting period (thin lines; cp. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#pone.0186556.g008" target="_blank">Fig 8B</a>). (D) CPs of 61 multiunits in LAC whose firing rate slowly increased during the waiting period (dashed curves; cp. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#pone.0186556.g008" target="_blank">Fig 8B</a>) and of 40 multiunits in LAC whose firing rate increased during the waiting period, also increased during the initial tones and then decreased during the intermittent tones (dotted curves).</p

Auditory categorization task.

<p>A trial started by turning on a cue light, which was the signal for the monkeys to grasp a touch bar. After a waiting period of 2220 ms, a sequence of up to ten tones started (black rectangles). Two types of tone sequences were used. The first type was composed of three initial tones with the same frequency followed by up to three tones of lower frequency. It consisted of one downstep (green square) and several frequency repeats of which the one marked by the blue square was taken to analyze category sensitivity of neurons. The second type was composed of three initial tones, followed by four intermittent tones of higher frequency, which were followed by up to three tones of lower frequency. This sequence thus also consisted of one upstep (red square) in addition to the downstep and the frequency repeats. The monkeys had to release the bar after the occurrence of a downstep (downward pointing arrow).</p

Distributions of phasic response increases in three regions of the auditory forebrain.

<p>Phasic response increases describe the temporal development of phasic response strengths within a trial (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#sec002" target="_blank">Methods</a>). Asterisks mark average phasic response increases significantly greater than 0 (t-tests, p < 0.01). All other conventions as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#pone.0186556.g004" target="_blank">Fig 4</a>.</p

Overview of the sample sizes used in the current report.

<p>Overview of the sample sizes used in the current report.</p

Percentage of multiunits with tonic responses in different brain regions of trained monkeys and of a control monkey.

<p>Percentage of multiunits with tonic responses in different brain regions of trained monkeys and of a control monkey.</p

Tonic response types in three regions of the auditory forebrain of trained monkeys.

<p>(A) Time course of the normalized firing rate of 82 multiunits in RAC whose firing rate slowly decreased during the waiting period. The two purple vertical bars mark the time windows that were used to select these multiunits. The vertical dashed line marks the onset of the 4th tone. The black curve was calculated from trials in which the monkey correctly responded to the downstep after the presentation of the intermittent tones. The relative frequency of response times is shown in the lower right histogram (black bars). The red curve was calculated from trials in which the monkeys incorrectly responded to the upstep. The relative frequency of incorrect response times is shown in the lower right histogram (red bars). The shaded curves reflect the standard errors of the mean for each of the two curves. The increased firing about 2000 to 2800 ms before sequence onset is related to bar grasping and to the onset of the cue light. Firing before bar grasping (marked by the arrow) is dispersed because bar grasps occurred after variable reaction times after the cue-light. (B) Results of 127 multiunits in LAC whose firing rate decreased during the waiting period. (C) Results of 26 multiunits in MGB whose firing rate decreased during the waiting period. (D) Results of 61 multiunits in LAC whose firing rate increased during the waiting period. (E) Results of 19 multiunits in MGB whose firing rate decreased during the initial tones of the sequence. (F) Results of 72 multiunits in LAC whose firing rate increased during the initial tones of the sequence. (G) Results of 11 multiunits in MGB whose firing rate increased during the intermittent tones of the sequence. (H) Results of 89 multiunits in LAC whose firing rate decreased during the intermittent tones of the sequence.</p

Similar preferences for downsteps in three regions of the auditory forebrain.

<p>(A) Distributions of phasic response strengths for downsteps, upsteps, and frequency repeats of 34 multiunits in right auditory cortex (RAC). Data from the same multiunit are connected by lines. The diamonds represent mean logarithmic strengths and the whiskers represent standard errors. Asterisks mark significant differences between pairs of tone steps (t-tests, p < 0.01). Phasic response strength was defined as the maximal normalized firing rate (see lower panels in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186556#pone.0186556.g003" target="_blank">Fig 3</a>). (B) Distributions of phasic response strengths for the three tone steps of 20 multiunits in right medial geniculate body (MGB). (C) Distributions of phasic response strengths for the three tone steps of 36 multiunits in left auditory cortex (LAC). (D) Distributions of phasic response strength for the three tone steps of 28 multiunits in the LAC of a control monkey who was naive to the categorization task and only passively exposed to the tone sequences.</p