Drinking songs: alcohol effects on learned song of zebra finches

Abstract

Speech impairment is one of the most intriguing and least understood effects of alcohol on cognitive function, largely due to the lack of data on alcohol effects on vocalizations in the context of an appropriate experimental model organism. Zebra finches, a representative songbird and a premier model for understanding the neurobiology of vocal production and learning, learn song in a manner analogous to how humans learn speech. Here we show that when allowed access, finches readily drink alcohol, increase their blood ethanol concentrations (BEC) significantly, and sing a song with altered acoustic structure. The most pronounced effects were decreased amplitude and increased entropy, the latter likely reflecting a disruption in the birds' ability to maintain the spectral structure of song under alcohol. Furthermore, specific syllables, which have distinct acoustic structures, were differentially influenced by alcohol, likely reflecting a diversity in the neural mechanisms required for their production. Remarkably, these effects on vocalizations occurred without overt effects on general behavioral measures, and importantly, they occurred within a range of BEC that can be considered risky for humans. Our results suggest that the variable effects of alcohol on finch song reflect differential alcohol sensitivity of the brain circuitry elements that control different aspects of song production. They also point to finches as an informative model for understanding how alcohol affects the neuronal circuits that control the production of learned motor behaviors.

Figure 1. The finch song system and experimental paradigm.

(A) The neuronal song system consists of a posterior vocal motor pathway (black): pre-motor cortical nucleus HVC projects to motor nucleus RA (robustus of the arcopallium), which projects to brainstem medullary nXIIts respiratory and vocal (syrinx) motor neurons, and the anterior pathway (white): HVC (a proper name), which projects to striatal Area X (X), and from there, sequentially to thalamic nucleus DLM (dorso-lateral division of the medial thalamus), to cortical nucleus LMAN (lateral magnocellular nucleus of the nidopallium) and to RA. (B) The study design assigned adult male finches to alcohol or control drinking treatments. They were then taken through three sequential Phases where they were provided with water (Phase I), 50% juice (Phase II), and alcohol in juice or juice only (Phase III).

Figure 2. Blood ethanol concentrations (BEC) in male zebra finches.

Birds were provided with 6.5% alcohol in 50% juice during Phase III of our experimental paradigm.

Figure 3. Effect of alcohol drinking on singing behavior.

Plotted are the individual and treatment group means of (A) number of lead notes per bout, (B) the mean number of motifs within a bout and (C) the mean number of bouts per hour across Phases for birds that received alcohol (red) in Phase III and for controls (blue). Small symbols connected by dotted lines represent individual bird means, while large symbols connected by solid lines represent the treatment groups. An * indicates a significant change across phases for both the control and alcohol treatments, combined.

Figure 4. Effects of alcohol drinking on song acoustic features.

Plotted are the values of least-square means of each acoustic feature (A–F) from whole-motif measurements of all individuals; error bars are standard errors of the means. * indicates a significant difference.

Figure 5. Principal Component Analysis (PCA) of the effects of alcohol drinking on acoustic parameters of whole song motifs.

A. Relative contributions of different acoustic parameters to PCA eigenvectors; the darkness of the print indicates the strength of contribution. B. Scree plot indicating the percent contribution by each eigenvector to the total variation along the axis. Plots of PC2 vs. PC1 for (C) the Alcohol treatment and (D) the Control treatment: unique colors denote individual birds; open and solid circles indicate daily values recorded in Phase II (no alcohol) and Phase III (alcohol) respectively; some individual values are not visible as they overlap.

Figure 6. Dose-relationships between BEC and motif-level (A) amplitude and (B) entropy.

The vertical axis is centered on residual values calculated around individual birds, and individual birds are represented by unique colors. The traces are spline fits (λ = 100,000).

Figure 7. Effects of alcohol drinking on individual song syllables.

Shown are sample spectrograms of single motifs from the same bird in the alcohol group, recorded during (A) Phase II (no alcohol) and (B) Phase III (alcohol); individual syllables are color-coded and labeled 1–4. (C) Plotted are mean values of acoustic features of each syllable during Phases II and III; error bars are Bonferroni-corrected 95% confidence intervals, * indicates significant differences between no alcohol and alcohol conditions.

Figure 8. Left: Syllable types in zebra finch song.

Shown are representative examples of (A) simple stacked (SS), (B) simple noisy (SN), (C) complex stacked (CS) and (D) complex noisy (CN) syllables. Simple stacked syllables are represented by single harmonics stacks or clear tones, whereas simple noisy syllables are single elements that lack well defined harmonic structure. Complex stacked types contain a combination of harmonic stacks and noisy elements, whereas complex noisy have multiple noisy elements but no harmonic stacks. Right: Effects of alcohol on zebra finch song syllable types. Direction of arrows indicate direction of change (up or down), dashes indicate lack of change. Frequencies of directional shifts are tallied at the bottom (yellow).

Figure 9. Effects of alcohol drinking on a specific zebra finch song syllable.

Shown are spectrograms of a representative syllable recorded in Phases II (no alcohol; left) and III (alcohol, mean BEC = 53.4 mg/dl; right) overlaid with traces of (A) amplitude, (B) pitch, and (C) Wiener entropy (respective scales on the right). For this syllable there were significant decreases in mean amplitude and pitch, and an increase in entropy under alcohol; other acoustic features did not change (not shown).