\documentclass{article}

\input{packages}

\begin{document}

\begin{table}
\begin{center}
{\bfseries\strut Transition probability between modes}
\begin{tabular}{cccc}
    \toprule
    \textbf{from/to:} & 
    \begin{tabular}{@{}c@{}}\textbf{leave}\end{tabular} & 
    \begin{tabular}{@{}c@{}}\textbf{drink}\end{tabular} &
    \begin{tabular}{@{}c@{}}\textbf{explore}\end{tabular} \\
    \midrule
    \bf{leave}    & & $0.51 \pm 0.14$ & $0.49 \pm 0.14$ \\
    \bf{drink}    & $0.10 \pm 0.05$ & & $0.90 \pm 0.05$ \\
    \bf{explore}    & $0.40 \pm 0.11$ & $0.60 \pm 0.11$ &  \\
    \bottomrule
\end{tabular}
\end{center}
\end{table}
\end{document}