Corrigendum: Cellular scaling rules for the brain of Artiodactyla include a highly folded cortex with few neurons

It has come to our attention that some of the data presented in Table 1, on the mass, numbers of neurons and densities of brain structures in Artiodactyla, required minor corrections. Specifically, while the legend informed that total values for the cerebral cortex included the hippocampus (as in our previous studies), we recently realized that values for the hippocampus had in four cases been included in the rest of brain, not cerebral cortex, in Table 1, and had failed to be included for Damaliscus. There were a few other minor mistakes in the table that are now also corrected in Table 1 below.

Table 1.

Cellular composition of Artiodactyla brains.

	Sus scrofa domesticus	Antidorcas marsupialis	Damaliscus dorcas phillipsi	Tragelaphus stripceros	Giraffa camelopardalis
MBD, kg	~100	25	60	218	470
MBR, g	64.180	106.074	154.718	306.860	537.218
MCxT, g	42.202	68.806	111.310	213.370	398.808
MHP, g	1.928	3.434	2.266	10.936	7.486
MCB, g	8.128	11.458	13.402	31.776	67.730
MRoB, g	13.850	25.810	30.006	61.716	70.680
MD+BG, g	6.728	12.194	n.a.	30.418	33.322
MMES, g	2.338	5.304	n.a.	12.902	15.928
MP+M, g	4.784	8.312	8.060	18.396	21.430
MOB, g	0.822	1.200	n.a.	5.546	2.052
NBR	2.22 × 109	2.72 × 109	3.06 × 109	4.91 × 109	10.75 × 109
NCxT	307.08 × 106	396.90 × 106	570.67 × 106	762.57 × 106	1.73 × 109
NGM	207.75 × 106	293.77 × 106	361.95 × 106	596.21 × 106	1.33 × 109
NHP	12.91 × 106	20.48 × 106	22.09 × 106	28.36 × 106	58.59 × 106
NCB	1.86 × 109	2.26 × 109	2.40 × 109	4.04 × 109	8.88 × 109
NRoB	58.71 × 106	70.48 × 106	86.43 × 106	106.59 × 106	142.70 × 106
ND+BG	34.40 × 106	40.12 × 106	n.a.	58.88 × 106	68.63 × 106
NMES	12.43 × 106	7.52 × 106	n.a.	26.07 × 106	26.63 × 106
NP+M	11.88 × 106	22.84 × 106	20.72 × 106	21.64 × 106	47.72 × 106
NOB	9.20 × 106	16.00 × 106	n.a.	38.33 × 106	24.68 × 106
DNCxT	7276	5768	5127	3574	4339
DNGM	7375	6684	5142	4644	5882
DNHP	6695	5965	9750	2594	8435
DNCB	228,632	196,999	179,206	127,218	131,080
DNRoB	4238	2731	2880	1727	2019
DND+BG	5113	3290	n.a.	1936	2060
DNMES	5317	1418	n.a.	2594	1672
DNP+M	2483	2748	2570	1176	2227
DNOB	11,187	13,332	n.a.	6912	12,026
O/NBR	2.111	2.170	3.054	3.456	3.526
O/NCXT	10.585	10.396	11.851	16.133	15.900
O/NGM	8.544	7.239	8.356	8.754	7.763
O/NHP	10.334	10.111	9.246	17.868	10.628
O/NCB	0.188	0.207	0.184	0.313	0.622
O/NRoB	18.682	18.710	24.718	31.980	34.190
O/ND+BG	17.779	19.408	n.a.	31.841	38.841
O/NMES	15.667	30.250	n.a.	30.546	41.017
O/NP+M	24.452	13.706	22.810	34.088	23.483
O/NOB	8.434	6.576	n.a.	8.523	9.417

Cellular composition of the five artiodactyl species. M, mass of body (M_BD) or brain structure; N, number of neurons; DN, neuronal density (in neurons/mg); O/N, ratio between numbers of other (non-neuronal) cells and neurons. BR, whole brain (excluding the olfactory bulb); CXT, whole cerebral cortex (gray matter, white matter and hippocampus); GM, gray matter of the cerebral cortex; HP, hippocampus; CB, cerebellum; RoB, rest of brain (the sum of diencephalon + basal ganglia, mesencephalon, and pons + medulla); D + BG, diencephalon + basal ganglia; MES, mesencephalon; P + M, pons + medulla; OB, olfactory bulb. All values refer to the two hemispheres together.

While these corrections do not modify in any way the conclusions of the paper, some of the power exponents reported were influenced in minor, non-significant ways. Those corrected power exponents are also provided below.

Corrections in text:

p. 4 – Brain mass varies 8.4-fold, number of brain neurons varies 4.8-fold.

Corrected relationships and power functions:

p. 4, Figure 3A – Brain mass increases as a power function of body mass with a small exponent of 0.548 ± 0.038 (p = 0.0048).

p. 4, Figure 3C – The total number of brain neurons increases as a power function of body mass with an exponent of 0.448 ± 0.115 (p = 0.0598).

p. 5 – The relative mass of the rest of brain does not decrease significantly with increasing brain mass (Spearman correlation, ρ = −0.800, p = 0.1041).

p. 7 – The cerebral cortex has only 15.7 ± 0.8% of all brain neurons, despite representing 69.5 ± 1.8% of brain mass, and the rest of brain, which accounts for 19.6 ± 1.8% of brain mass, has only 2.3 ± 0.3% of all brain neurons.

p. 7, Figure 4A – Total brain mass varies as a power function of its number of neurons with an exponent of 1.288 ± 0.215 (r² = 0.923, p = 0.0093).

p. 7, Figure 4B – The relationship between the mass of the cerebral cortex and its number of neurons has an exponent of 1.303 ± 0.154 (p = 0.0035) including the giraffe, and 1.721 ± 0.123 (r² = 0.990, p = 0.0051) excluding the giraffe.

p. 7, Figure 4D – The mass of the rest of brain scales as a power function of its number of neurons across artiodactyls with an exponent of 1.850 ± 0.303 (r² = 0.925, p = 0.0089).

p. 7, Figure 5A – The relationship between mass of each brain structure (cerebral cortex, cerebellum and rest of brain) and number of other (non-neuronal) cells can be described as a single power function of exponent 0.859 ± 0.047 (p < 0.0001).

p. 7, Figure 5B – Whole brain mass varies as a similar function of numbers of other cells across artiodactyls (exponent 0.986 ± 0.089, p = 0.0016) (…) and all clades together (exponent, 1.040 ± 0.020, p < 0.0001).

p. 8 – Neuronal density in the cerebral cortex (gray + white matter + hippocampus) varies between 3574 neurons/mg in the greater kudu to 7276 neurons/mg in the pig (…) and in the rest of brain, from 1727 neurons/mg in the greater kudu to 4238 neurons/mg in the pig. p. 9, Figure 6A – Neuronal density in the artiodactyl cerebral cortex (minus the giraffe) decreases with increasing cortical mass, as a power function of exponent −0.425 ± 0.041 (p = 0.0093).

p. 9, Figure 6A – In the rest of brain, neuronal density also decreases significantly as a power function of increasing structure mass (exponent, −0.500 ± 0.082, p = 0.0089).

p. 10, Figure 7 – The O/N ratio varies between 0.184 (in the blesbok cerebellum) and 34.190 (in the giraffe rest of brain). The O/N ratio varies within the cortical gray matter alone between 7.2 and 8.8 across species.

p. 10, Figure 7B – The O/N ratio varies as a common power function of neuronal density across all artiodactyl structures with an exponent of −1.087 ± 0.032 (p < 0.0001).

p. 10 – The addition of artiodactyl structures does not change the exponent significantly (−0.935 ± 0.021, p < 0.0001).

p. 11 – N/A is 2–6 times smaller in artiodactyls (19,902 ± 1253 neurons/mm²) than in primates.

p. 11, Figure 8C – Cortical surface area increases with numbers of neurons raised to an exponent of 1.362 ± 0.094 across artiodactyls (p = 0.0047).

p. 11 – Gray matter thickness increases with number of cortical neurons raised to the power of 0.630 ± 0.089 in artiodactyls (minus the giraffe; p = 0.0192).

p. 13 – Predictions for cetaceans: The prediction is given by the equation N_CXT = e^{17.168±0.053}. M^0.633±0.024_CXT.

p. 14 – Using the cortical volume given (…) we predict the cerebral cortex (…) to be composed of 1.14, 1.99, 2.44, and 3.56 billion neurons, respectively.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.