Recent advances in the stellar population studies of unresolved galaxies in the NIR domain demonstrated that it contains several line-strength indices to be potentially used as diagnostics for stellar population properties. Reduction of the extinction and possibility to disentangle different stellar populations dominating different spectral ranges are obviously beneficial. To this aim, we have investigated the connections between 19 Lick/IDS indices and 39 NIR indices measured in the central regions of 32 galaxies observed with X-shooter. We adopted a systematic approach to deriving a correlation matrix using all the optical and NIR indices measured for the galaxies and building new NIR composite indices to maximize their correlations with the best age and metallicity optical tracers. We found that the new T1 and [AlFeCr] composite indices are promising age and metallicity diagnostics in NIR, respectively. We finally tested the T1 and [AlFeCr] indices with the predictions of simple stellar populations models, and we found that the models show a general agreement with the data. Some fine tuning and further comparison between models and data, which are now largely available, is necessary to reach the prediction level of the optical line-strength indices. C1 [Gasparri, D.; Morelli, L.; Cuomo, V] Univ Atacama, Inst Astron & Ciencias Planetarias, Copayapu 485, Copiapo, Chile. [Morelli, L.] INAF Osservatorio Astron Brera, Via Brera 28, I-20121 Milan, Italy. [Ivanov, V. D.; Coccato, L.] European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany. [Ivanov, V. D.] European Southern Observ, Ave Alonso de Cordova 3107, Vitacura, Santiago, Chile. [Pizzella, A.; Corsini, E. M.; Dalla Bonta, E.] Univ Padua, Dipartimento Fis & Astron G Galilei, Vicolo Osservatorio 3, I-35122 Padua, Italy. [Pizzella, A.; Corsini, E. M.; Dalla Bonta, E.] INAF, Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua, Italy. [Francois, P.] Univ Paris Diderot, PSL Res Univ, CNRS, Sorbonne Paris Cite,GEPI,Observ Paris, 61 Ave Observ, F-75014 Paris, France. [Corsini, E. M.] CSIC, Ctr Astrobiol CAB, INTA, Ctra Ajalvir km 4, E-28850 Torrejon De Ardoz, Madrid, Spain. [Dalla Bonta, E.] Univ Cent Lancashire, Jeremiah Horrocks Inst, Preston PR1 2HE, England. [Mendez-Abreu, J.; Aguerri, J. A. L.] Inst Astrofis Canarias, C Via Lactea S-N, E-38200 San Cristobal la Laguna, Spain. [Mendez-Abreu, J.; Aguerri, J. A. L.] Univ La Laguna, Dept Astrofis, C Astrofis Francisco Sanchez, E-38205 San Cristobal la Laguna, Spain. C3 Universidad de Atacama; Istituto Nazionale Astrofisica (INAF); European Southern Observatory; European Southern Observatory; University of Padua; University of Padua; Istituto Nazionale Astrofisica (INAF); Universite PSL; Observatoire de Paris; Universite Paris Cite; Centre National de la Recherche Scientifique (CNRS); Consejo Superior de Investigaciones Cientificas (CSIC); CSIC - Centro de Astrobiologia (INTA); University of Central Lancashire; Instituto de Astrofisica de Canarias; Universidad de la Laguna